Objective for an endoscope

ABSTRACT

An objective for an endoscope comprising, in the order from the object side, a first lens unit I having negative refractive power, a second lens unit II having positive refractive power, a third lens unit III having positive refractive power, an aperture stop S arranged between the front end of the second lens unit and rear end of the third lens unit and a fourth lens group IV comprising a lens component which has a concave surface on the object side, the four unit objective for an endoscope being arranged so that the overall length is short, outer diameter of the objective is small, angle of view is wide, intensity of light in the marginal portion is high, and distortion is corrected favourably.

BACKGROUND OF THE INVENTION

(a) Field of the Invention

The present invention relates to an objective for an endoscope.

(b) Description of the Prior Art

A retrofocus type lens system disclosed in U.S. Pat. No. 4,037,938 andhaving a lens configuration as shown in FIG. 1 is known as an objectivefor an endoscope. Said known objective comprises a front subsystem Fhaving negative refractive power, and a rear subsystem R having positiverefractive power, and the lens system as a whole is arranged as atelecentric type lens system by providing a stop S at the front focalpoint of the rear subsystem. Said known objective has a strong pointthat the loss of light to be caused in the image guide fiber bundle 1 issmall because the prinicpal ray 2 vertically enters the light entrancesurface of the image guide fiber bundle 1. However, as said objective iscomposed in such lens type that is considerably asymmetrical in respectto the stop S, distortion occurs largely. Moreover, as said objective isarranged as a telecentric type lens system, the outer diameter of thelens system is large compared with the image height.

On the other hand, a symmetrical type lens system disclosed in U.S. Pat.No. 2,781,695 and having a lens configuration as shown in FIG. 3 isknown as a lens system whose distortion is very small. Said known lenssystem is arranged to be perfectly symmetrical in respect to the stop Sas it will be understood also from FIG. 3 and, therefore, distortion tobe caused is very small. However, due to the fact that the lens systemis symmetrical, the incident angle on the first lens component L₁ isequal to the emerging angle from the fourth lens component L₆ and,therefore, the incident angle of the principal ray with a large angle ofview which is incident on the image surface becomes considerably large.As a result, the intensity of light in the marginal portion decreasesdue to the cos⁴ law.

Furthermore, modified symmetrical type lens systems are also known asdisclosed in U.S. Pat. No. 3,209,646 and U.S. Pat. No. 4,176,915. Saidknown lens systems have the basic power distribution similar to that ofthe lens system shown in FIG. 3, i.e., a negative and positive lenscomponents are arranged in front of the stop and a positive and negativelens components are arranged in rear of the stop. Besides, shapes ofindividual lens components arranged in front of the stop aresubstantially the same as those of individual lens components arrangedin rear of the stop.

SUMMARY OF THE INVENTION

It is, therefore, a primary object of the present invention to providean objective for an endoscope arranged that distortion is comparativelysmall, the lens system as a whole is compact and, at the same time, thedecrease in the intensity of light in the marginal portion is small.

The objective for an endoscope according to the present invention has abasic four unit lens configuration as shown in FIG. 2 and comprises afirst lens unit I having negative refractive power, a second lens unitII having positive refractive power, a third lens unit III havingpositive refractive power, an aperture stop S arranged at a positionbetween the front end of said second lens unit II and rear end of saidthird lens unit III, and a fourth lens unit IV comprising a lenscomponent having a concave surface on the object side, said objectivefor an endoscope being arranged to comprise at least three positive lenscomponents, including a cemented doublet, which are respectively locatedat positions between the front end of said second lens unit II and rearend of said fourth lens unit IV. In FIG. 2, reference symbol 3represents, for example, a solid-state image pick-up device.

In case of the basic four unit lens configuration described in theabove, it is possible to reduce distortion to be caused compared withthe retrofocus type lens systems by providing the fourth lens unit IVcomprising a meniscus lens, which is convex toward the image side, onthe image side of the aperture stop and thereby increasing the symmetryof the lens system as a whole in respect to the aperture stop. Moreover,as the aperture stop is arranged at a position between the front end ofthe second lens unit II and rear end of the third lens unit III asdescribed in the above, the aperture stop comes to a position on theimage side of the front focal point of a total system which is formed bythe second, third and fourth lens units (II, III and IV). As a result,the four unit lens system as a whole does not become a telecentric typelens system and, therefore, it is possible to make the outer diameter ofthe lens system small compared with the image height.

Furthermore, when the aperture stop is located between the second lensunit II and third lens unit III as shown in FIG. 2, a positive lens unitcomes to a position in front of the aperture stop. Consequently, theasymmetry of the four unit lens system is reduced, and this ispreferably also for correction of distortion and coma.

Besides, by arranging at least three positive lens components atpositions between the front end of the second lens unit II and rear endof said fourth lens unit IV, the incident angle of the principal ray onthe image surface is made small so as to thereby prevent the decrease inthe intensity of light in the marginal portion to be caused due to thecos⁴ law.

As described so far, by combining the strong points of the retrofocustype lens systems and those of the symmetrical type lens systems, thepresent invention materializes an objective for an endoscope which isarranged favourably from all of the view points of correction ofdistoration, compactness of the lens system, and intensity of light inthe marginal portion.

To attain the object of the present invention, it is more preferable toarrange that the objective for en endoscope according to the presentinvention having the above-mentioned basic four unit lens configurationfulfills the condition (1) shown below:

    |h.sub.1 /f.sub.5 |<1.15|h.sub.4 /f.sub.4 |                                                (1)

where, reference symbol h₁ represents the mean value of heights ofprincipal rays on respective surfaces of the first lens unit I,reference symbol h₄ represents the mean value of heights of principalrays on respective surfaces of the fourth lens unit IV, reference symbolf₁ represents the focal length of the first lens unit I, and referencesymbol f₄ represents the focal length of the fourth lens unit IV.

The condition (1) shown in the above defines the ratio between therefractive power of the first and fourth lens units in order to arrangethat the available incident angle of the principal ray on the first lensunit I becomes wider, the principal ray is adequetely refracted by thefourth lens unit IV, and distortion is thereby eliminated in the rangewhere the intensity of light in the marginal portion does not decreaseso much, and in order to arrange that the overall length (length fromthe first surface of the lens system to the image surface) becomes shortand outer diameter of the objective becomes small. To attain theabove-mentioned purpose, the focal length f₁ of the first lens unit Iand focal length f₄ of the fourth lens unit IV should be selected so asto fulfill the condition (1) shown in the above. When the condition (1)is not fulfilled, distortion cannot be corrected and, moreover, the lenssystem becomes large.

In addition to the condition (1) described in the above, it ispreferable to arrange that the objective for an endoscope according tothe present invention further fulfills the condition (2) shown below:

    f.sub.2 <9f                                                (2)

where, reference symbol f₂ represents the focal length of the secondlens unit II, and reference symbol f represents the focal length of thelens system as a whole.

When the lens system is arranged to fulfill the condition (2), it hassuch effect that the positive refractive power thereof is shifted towardthe front portion of the lens system. As a result, the principal pointof the lens system as a whole is shifted toward the object side, and itis possible to make the overall length of the lens system short.Besides, it is possible to correct coma to be caused by lower rays atthe first lens unit I which has negative refractive power.

When the condition (2) is not fulfilled, it is difficult to correctcoma.

In addition to the conditions (1) and (2), it is preferable to arrangethat the objective for an endoscope according to the present inventionfurther fulfills the conditions (3), (4), (5) and (6) shown below:

    |f.sub.1 |<5f                            (3)

    |f.sub.23 |<4.5f                         (4)

    |f.sub.a /f.sub.b |<30                   (5)

    R.sub.2 >0                                                 (6)

where, reference symbol f₂₃ represents the total focal length of thesecond lens unit II and third lens unit III, reference symbols f_(a) andf_(b) respectively represent the largest value and smallest value out ofthe focal lengths of said at least three positive lens componentsincluding a cemented doublet which are respectively arranged atpositions between the front end of the second lens unit II and rear endof the fourth lens unit IV, and reference symbol R₂ represents theradius of curvature of the foremost surface (surface on the object side)of the second lens unit II.

In a four unit lens system which fulfills the conditions (3) and (4)shown in the above, the negative refractive power of the first lens unitI and positive refractive powers of the second lens unit II and thirdlens unit III become comparatively strong, and this is preferableespecially for making the overall length of the lens system short.However, if the above-mentioned refractive powers are made too strong,the overall length of the lens system becomes too short. As a result,the incident angle of the principal ray on the image surface becomeslarge, and the intensity of light in the marginal portion decreasesconsiderably. Therefore, it is preferable to arrange that |f₂₃ | isselected in the range of f<|f₂₃ |. When the conditions (3) and/or (4) isnot fulfilled, it is difficult to make the overall length of the lenssystem short.

When refractive powers of the above-mentioned lens units are made strongso that the conditions (3) and (4) are fulfilled, it becomes difficultto correct aberrations. Especially, in case that the field angle is wideand the aperture stop S is located at a position between the foremostsurface of the second lens unit II and rearmost surface of the thirdlens unit III, correction of aberrations becomes more difficult. Toeliminate the above-mentioned difficulty, it is preferable to fulfillthe conditions (5) and (6).

The condition (5) defines the power distribution of positive refractivepower in the lens system. When the positive refractive power is alloted,as defined by the condition (5), to at least three positive lenscomponents including a cemented doublet, which are respectively arrangedat positions between the front end of the second lens unit II and rearend of the fourth lens unit IV, it becomes possible to correctaberrations. When the condition (5) is not fulfilled, it becomesdifficult to correct aberrations.

The condition (6) defines the radius of curvature of the foremostsurface (surface on the object side) of the second lens unit II. Bymaking said radius of curvature positive, it is possible to preventincident angle of offaxial rays on said surface from becomingexcessively large and to thereby prevent the astigmatic difference fromoccurring. When the condition (6) is not fulfilled, the astigmaticdifference becomes large.

To obtain an objective for an endoscope which is more suitable forattaining the object of the present invention, it is preferably tofurther fulfill the conditions (7) and (8) shown below:

    -R.sub.2 '≦15f                                      (7)

    R.sub.3 ≦30f                                        (8)

where, reference symbol R₂ ' represents the radius of curvature of therearmost surface (surface on the image side) of the second lens unit II,and reference symbol R₃ represents the radius of curvature of theforemost surface (surface on the object side) of the third lens unitIII.

When either the condition (7) or the condition (8) is not fulfilled,spherical aberration will be undercorrected.

Furthermore, when an aspherical surface is adopted in the objective foran endoscope according to the present invention, it is possible tocorrect distortion and curvature of field satisfactorily favourable. Thereason thereof is as described below.

The known objective for an endoscope shown in FIG. 1 causes remarkablenegative distortion. This is because, when the principal ray is tracedinversely from the image side, the principal ray is refracted asdescribed below. That is, when it is supposed that the lens system as awhole is divided into a front subsystem located in front of the aperturestop S and a rear subsystem located in rear of the aperture stop S, theprincipal ray traced inversely is refracted by the front subsystemlocated in front of the aperture stop S and rear sybsystem located inrear of the aperture stop S in such direction that the angle of view iswidened as the image height increases. Therefore, it is possible tocorrect said remarkable negative distortion when the lens system isprovided with an aspherical surface whose refractive power for theprincipal ray is made weaker toward the portions farther from theoptical axis.

For this purpose, the lens system may be so arranged that either thesurface on the object side of at least one of lens componentsconstituting the front subsystem located in front of the aperture stop Shas such portions whose curvature becomes gradually stronger as they arefarther from the optical axis or the surface on the image side of atleast one of lens components constituting the front subsystem located infront of the aperture stop S has such portions whose curvature becomesgradually weaker as they are farther from the optical axis or the lenssystem may be so arranged that either the surface on the object side ofat least one of lens components constituting the rear subsystem locatedin rear of the aperture stop S has such portions whose curvature becomesgradually weaker as they are farther from the optical axis or thesurface on the image side of at least one of lens componentsconstituting the rear subsystem located in rear of the aperture stop Shas such portions whose curvature becomes gradually stronger as they arefarther from the optical axis. Thus, it is possible to correctdistortion and curvature of field favourably.

As examples of the above-mentioned curved surface having portions whosecurvature becomes gradually stronger as they are farther from theoptical axis, shapes as shown in FIGS. 4 and 5 are also effective. Theword "curvature" used herein should be interpreted as a term including apositive or negative sign. Speaking correctly, curvature at an arbitrarypoint on a lens surface should be considered as negative when the centerof curvature of a spherical surface, which is in contact with said lenssurface at said arbitrary point, is located on the object side of saidlens surface or as positive when said center of curvature is located onthe image side of said lens surface. Accordingly, the shape shown inFIG. 4 is an example of a curved surface whose curvature including thesign increases toward the portions farther from the optical axis(increases from negative curvature of concavity on the object side topositive curvature of convexity on the object side), while the shapeshown in FIG. 5 is an example of a curved surface whose curvature onceincreases and then decreases toward the portions farther from theoptical axis.

The reason why the aspherical surface with a shape as shown in FIG. 5 isalso effective for correction of distortion is that, even when thedistortion curve has an unduration as shown in FIG. 6, it causes noproblem in practical use and that the marginal portion of the asphericalsurface shown in FIG. 5 has no relation to correction of distortionsince the principal ray does not pass through the marginal portionthough the lower rays pass.

Shapes as shown in FIGS. 7 and 8 may be included as examples of thecurved surface which has the portions whose curvature becomes graduallyweaker as they are farther from the optical axis and which may be usedfor a surface on the image side of a lens component.

As described so far, the aspherical surface to be provided in the frontsubsystem of the objective for an endoscope according to the presentinvention is to be formed, when it is used as a surface on the objectside of a lens component, as a surface whose curvature becomes graduallystronger at least at portions thereof including such surfaces as shownin FIGS. 4 and 5 and is to be formed, when it is used as a surface onthe image side of a lens component, as a surface whose curvature becomesgradually weaker at least at portions thereof including such surfaces asshown in FIGS. 7 and 8.

On the other hand, the aspherical surface to be provided in the rearsubsystem of the objective for an endoscope according to the presentinvention is to be formed, when it is used as a surface on the objectside of a lens component, as a surface whose curvature becomes graduallyweaker at least at portions thereof including such surfaces as shown inFIGS. 7 and 8 and is to be formed, when it is used as a surface on theimage side of a lens component, as a surface whose curvatrue becomesgradually stronger at least at portions thereof including such surfacesas shown in FIGS. 4 and 5.

When an objective includes at least one of the aspherical surfacesdescribed in the above, it is possible to correct distortion favourably.

In case that it is desired to correct distortion only, it is sufficientwhen one of the above-mentioned aspherical surfaces is provided on onlyone side of the aperture stop. In that case, however, swelling ofmeridional curvature of field at the intermediate image height becomeslarge and, consequently, the quality of image at the intermediate imageheight decreases considerably. This problem can be solved when theabove-mentioned aspherical surfaces are arranged in both of the frontand rear subsystems. That is, when so arranged, it is possible toeliminate the above-mentioned swelling of meridional curvature of fieldbecause the sign of the swelling of meridional curvature of field to becaused by the aspherical surface arranged in the front subsystem, i.e.,the "minus" sign, is inverse to the sign of the swelling of meridionalcurvature of field to be caused by the aspherical surface arranged inthe rear subsystem, i.e., the "plus" sign, and the meridional curvatureof field caused in the front subsystem is offset by the meridionalcurvature of field caused in the rear subsystem.

Now, the shape of the aspherical surface required for correction ofdistortion is quantitatively described below.

An aspherical surface can generally be expressed by the followingformula (9): ##EQU1## where, reference symbols x and y respectivelyrepresent values of coordinates in the coordinate system where theoptical axis is traced as the x axis taking the image direction aspositive and the y axis is traced perpendicularly to the x axis takingthe intersecting point between the aspherical surface and optical axisas the origin O, reference symbol C represents the inverse number of theradius of curvature of the spherical surface which is in contact withthe aspherical surface at a position near the optical axis, referencesymbol P represents a parameter representing the shape of the asphericalsurface, and reference symbols B, E, F, G, . . . respectively representthe coefficients of aspherical surface of the second order, fourthorder, sixth order, eighth order and so on.

When P=1 and all of B, E, F, G, . . . are zero in the formula (9) shownin the above, the surface expressed by the formula (9) is a sphericalsurface.

Besides, Seidel aberration coefficients are defined as expressed by theformulae (10) and (11) shown below. These are the same as those used inthe universal lens design program ACCOS-V. However, in case of ACCOS-V,the height of paraxial ray H₀ incident on the first surface of the lenssystem is determined by the following formula where the object distance(distance from the object point to the first surface of the lens system)is represented by reference symbol OB, numerical aperture of marginalray is represented by reference symbol NA, and refractive index of themedium existing on the object side of the first surface of the lenssystem is represented by reference symbol n₀. ##EQU2## On the otherhand, in the present invention, said height of paraxial ray H₀ isdetermined by the following formula. ##EQU3## Therefore, in the presentinvention, aberration coefficients are obtained by performing raytracing based on the paraxial theory by using the value of H₀ which isdetermined by the latter formula shown in the above.

For the meridonial ray (X=0) ##EQU4##

For the sagittal ray (Y=0): ##EQU5##

The formula (10) shown in the above is formulated by arranging that thedifference between the paraxial image point (image point when thereexists no aberration) of meridional rays and actual image point ofmeridional rays is represented by reference symbol ΔY. In the formula(10), reference symbol Y represents the incident height of paraxialprincipal ray on the image surface normallized by the maximum imageheight, and reference symbol H represents the incident height ofmarginal ray on the pupil surface normallized by the pupil diameter. Theformula (11) shown in the above is formulated in the same way as abovebut for the sagittal rays. Besides reference symbols SA3, SA5 and SA7respectively represent spherical aberrations of the third, fifth andseventh orders, reference symbols CMA3 and CMA5 respectively representtangential comae of the third and fifth orders, reference symbols AST3and AST5 respectively represent astigmatisms of the third and fifthorders, reference symbols PTZ3 and PTZ5 respectively represent Petzval'ssums of the third and fifth orders, reference symbols DIS3 and DIS5respectively represent distortions of the third and fifth orders,reference symbol TOBSA represents skew tangential spherical aberrationof the fifth order, reference symbol ELCMA represents elliptical coma ofthe fifth order, and reference symbol SOBSA represents skew sagittalspherical aberration of the fifth order.

Swelling of meridional curvature of field, which occurs when anaspherical surface is provided in a lens system, is caused by thedeviation of the aspherical surface from the spherical surface and iscaused due to the fact that the ratio of the value of the coefficient ofastigmatism A of the third order to the coefficient of astigmatism ofthe fifth order in the formulae (10) and (11) of Seidel aberrationcoefficients shown in the above is large compared with that of thespherical surface. Therefore, the astigmatism caused by the asphericalsurface provided in the front subsystem should be offset by theaspherical surface provided in the rear subsystem.

That is, when the sums A_(F) and A_(R) of the coefficients ofastigmatism is expressed by the formulae (12) and (13) shown below,where reference symbol A_(Fi) represents the value obtained when thecoefficient of astigmatism A to be caused by deviation of the asphericalsurface, which is formed on ith surface out of respective lens surfacesin the front subsystem, from the spherical surface is divided by Fnumber, and reference symbol A_(Rj) represents the value obtained whenthe coefficient of astigmatism A to be caused by the deviation of theaspherical surface, which is formed on jth surface out of respectivelens surfaces in the rear subsystem, from the spherical surface isdivided by F number, ##EQU6## it is necessary to arrange that the valueof A_(FR) given by the following formula (14) becomes a value close tozero.

    A.sub.FR =A.sub.F +A.sub.R                                 ( 14)

When the content shown by the formula (14) is expressed by otherformulae, it is possible to express said content as shown by thefollowing formulae (15) and (16).

    A.sub.F ·A.sub.R <0                               (15)

    |A.sub.F /A.sub.R |≈1            (16)

When the values of A_(F), A_(R) and A_(F) /A_(R) shown in the formulae(15) and (16) are calculated by using the lens system shown in FIG. 26as an example, they become as shown below.

    A.sub.F =-0.01851

    A.sub.R =0.01024

    A.sub.F /A.sub.R =1.808

As it will be evident from preferred embodiments shown later, it ispossible to correct aberrations satisfactorily favourably for practicaluse even when the value of |A_(F) /A_(R) | is not exactly 1. That is, itis allowable as far as said value comes into the range defined by thefollowing formula (17)

    0.01<|A.sub.F /A.sub.R |>20              (17)

In other words, when the shapes of the aspherical surfaces are decidedso as to fulfill the formulae (15) and (17), it is possible to obtain anobjective for an endoscope whose curvature of field is correctedfavourably and distortion is small.

The coefficient of astigmatism A_(i) of the third order to be caused bythe deviation of the aspherical surface, which is formed on ith surface,from the spherical surface is expressed by the formula (18) shown belowwhen P=1:

    A.sub.i =8h.sub.a.sup.2 h.sub.b.sup.2 ·E(N.sub.i -N.sub.i+1) (18)

where, reference symbols h_(a) and h_(b) respectively represent heightsof paraxial ray and paraxial principal ray on ith surface, referencesymbol E represents the coefficient of aspherical surface of the fourthorder of ith surface, and reference symbols N_(i) and N_(i+1)respectively represent refractive indices of media existing on theobject side and image side of ith surface.

Here, an aspherical surface may be provided to a cemented surfacebetween two lens elements. In that case, when the lens element with thelower refractive index is regarded as the air side, the shape of theaspherical surface can be decided in the same way as described in theabove, and it is possible to obtain an aspherical surface that serves toattain the object of the present invention.

Furthermore, in case that aspherical surfaces are provided respectivelyin the front subsystem located in front of the aperture stop and rearsubsystem located in rear of the aperture stop and, moreover, each ofthem is formed as an aspherical surface expressed by the formula ofaspherical surface which includes the coefficients of aspherical surfaceof the sixth and higher orders, said coefficients of aspherical surfaceof the sixth and higher orders can also contribute to elimination ofcurvature of field.

When ith surface is formed as an aspherical surface and the height ofprincipal ray on that aspherical surface is represented by referencesymbol h_(i) and when B_(i) =0 and P_(i) =0, the value of Q_(i)expressed by the formula (19) shown below is approximately proportionalto the value of curvature of field to be caused by the asphericalsurface on ith surface.

    Q.sub.i =(N.sub.i -N.sub.i+1){Eh.sub.i.sup.2 +Fh.sub.i.sup.4 +Gh.sub.i.sup.6 + . . . }                                 (19)

To arrange that the curvature of field caused by the aspherical surfacesprovided in front of the aperture stop and curvature of field caused bythe aspherical surfaces provided in rear of the aperture stop offseteach other, when the sum of Q_(i) in the front subsystem is representedby reference symbol Q_(F) and sum of Q_(i) in the rear subsystem isrepresented by reference symbol Q_(R), the formula (20) shown belowshould be fulfilled.

    Q.sub.S =Q.sub.F +Q.sub.R ≈0                       (20)

This means that, when either Q_(F) or Q_(R) which has the largerabsolute value out of them is represented by reference symbol Q_(M), thevalue of Q_(h) given by the formula (21) shown below is satisfactorilysmall.

    |Q.sub.S /Q.sub.M |=Q.sub.h              ( 21)

In other words, it is preferable to arrange that the value of Q_(h)becomes a value close to zero as in cases of Embodiments 20 through 22shown later. For practical use, it is allowable when Q_(h) fulfills thecondition (22) shown below.

    0≦Q.sub.h <4                                        (22)

Generally, distortion occurs largely at a surface where the height ofprincipal ray is large. Therefore, for correction of distortion, it ispreferable to provide an aspherical surface to a surface where theheight of principal ray is large. In other words, it is preferable toprovide the aspherical surface in the first lens unit I and/or fourthlens unit IV which are far from the aperture stop, especially, at aposition near the first lens component and/or a position near therearmost lens component.

For the manufacturing of an aspherical surface, it is preferable toadopt plastic molding or glass molding from the view point of the cost.Especially, lenses manufactured by glass molding are more preferablebecause they are more excellent in chemical resistance and the likecompared with lenses manufactured by plastic molding.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a sectional view of a known objective for an endoscope;

FIG. 2 shows the basic four unit lens configuration of the objective foran endoscope according to the present invention;

FIG. 3 shows a sectional view of a symmetrical type lens system;

FIGS. 4 and 5 respectively show sectional views illustrating examples ofaspherical lenses applicable to the objective for an endoscope accordingto the present invention;

FIG. 6 shows a graph illustrating an example of distortion;

FIGS. 7 and 8 respectively show sectional views illustrating otherexamples of aspherical lenses applicable to the objective for anendoscope according to the present invention;

FIG. 9 shows a coordinate system for illustrating the formula whichexpresses the shape of an aspherical surface;

FIGS. 10 through 31 respectively show sectional views of Embodiments 1through 22 of the objective for an endoscope according to the presentinvention; and

FIGS. 32 through 53 respectively show graphs illustrating aberrationcurves of Embodiments 1 through 22 of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Now, preferred embodiments of the objective for an endoscope accordingto the present invention are shown below.

    ______________________________________                                        Embodiment 1                                                                  ______________________________________                                        f = 1, F.sub.No = 3.018, 2ω = 100.926°                           IH = 0.9184                                                                   ______________________________________                                        r.sub.1 = 4.4097                                                              d.sub.1 = 0.2877 n.sub.1 = 1.88300                                                                          ν.sub.1 = 40.78                              r.sub.2 = 0.7457                                                              d.sub.2 = 1.0472                                                              r.sub.3 = 2.0242                                                              d.sub.3 = 0.3049 n.sub.2 = 1.74100                                                                          ν.sub.2 = 52.68                              r.sub.4 =0 ∞                                                            d.sub.4 = 0.3510                                                              r.sub.5 = ∞                                                             d.sub.5 = 0.3049 n.sub.3 = 1.74100                                                                          .sup.  .sub.3 = 52.68                           r.sub.6 = -2.0242                                                             d.sub.6 = 0.0575                                                              r.sub.7 = ∞ (aperture stop)                                             d.sub.7 = 0.0575                                                              r.sub.8 = 1.6116                                                              d.sub.8 = 0.5696 n.sub.4 = 1.51633                                                                          ν.sub.4 = 64.15                              r.sub.9 = -1.0213                                                             d.sub.9  = 0.2301                                                                              n.sub.5 = 1.80518                                                                          ν.sub.5 = 25.43                              r.sub.10 = -2.1617                                                            d.sub.10 = 0.0575                                                             r.sub.11 = ∞                                                            d.sub.11 = 0.2877                                                                              n.sub.6 = 1.53172                                                                          ν.sub.6 = 48.90                              r.sub.12 = ∞                                                            d.sub.12 = 0.3625                                                             r.sub.13 = -0.8009                                                            d.sub.13 = 0.2301                                                                              n.sub.7 = 1.72825                                                                          ν.sub.7 = 28.46                              r.sub.14 = -1.3705                                                            d.sub.14 = 0.3855                                                             r.sub.15 = ∞                                                            d.sub.15 = 0.5754                                                                              n.sub.8 = 1.51633                                                                          ν = 64.15                                    r.sub.16 = ∞                                                            ______________________________________                                        |h.sub.1 /f.sub.1 | = 0.6308, 1.15|h.sub.4         /f.sub.4 | = 0.1670                                                  f.sub.2 = 1.567, f.sub.1 = -1.055, f.sub.23 = 1.179                           f.sub.a /f.sub.b = 2.732/2.526 = 1.082, R.sub.2 = 2.024                       R.sub.2 '  = -2.024, R.sub.3 = 1.612                                          ______________________________________                                    

    ______________________________________                                        Embodiment 2                                                                  ______________________________________                                        f = 1, F.sub.No = 3.102, 2ω = 100.03°                            IH = 0.9142                                                                   ______________________________________                                        r.sub.1 = 3.6033                                                              d.sub.1 = 0.2864 n.sub.1 = 1.88300                                                                          ν.sub.1 = 40.78                              r.sub.2 = 0.7446                                                              d.sub.2 = 1.0439                                                              r.sub.3 = 1.9155                                                              d.sub.3 = 0.3136 n.sub.2 = 1.74100                                                                          ν.sub.2 = 52.68                              r.sub.4 = 13.9967                                                             d.sub.4 = 0.3855                                                              r.sub.5 = -13.9967                                                            d.sub.5 = 0.3136 n.sub.3 = 1.74100                                                                          ν.sub.3 = 52.68                              r.sub.6 = -1.9155                                                             d.sub.6 = 0.0573                                                              r.sub.7 = ∞ (aperture stop)                                             d.sub.7 = 0.0573                                                              r.sub.8 = 1.3927                                                              d.sub.8 = 0.6192 n.sub.4 = 1.51633                                                                          ν.sub.4 = 64.15                              r.sub.9 = -0.9683                                                             d.sub.9 = 0.2291 n.sub. 5 = 1.80518                                                                         ν.sub.5 = 25.43                              r.sub.10 = -1.9872                                                            d.sub.10 = 0.0573                                                             r.sub.11 = ∞                                                            d.sub.11 = 0.2864                                                                              n.sub.6 = 1.53172                                                                          ν.sub.6 = 48.90                              r.sub.12 = ∞                                                            d.sub.12 = 0.3023                                                             r.sub.13 = -0.8271                                                            d.sub.13 = 0.2291                                                                              n.sub.7 = 1.72825                                                                            = 28.46                                       r.sub.14 = -1.4614                                                            d.sub.14 = 0.5727                                                             r.sub.15 = ∞                                                            d.sub.15 = 0.2864                                                                              n.sub.8 = 1.51633                                                                          ν.sub.8 = 64.15                              r.sub.16 = ∞                                                            ______________________________________                                        |h.sub.1 /f.sub.1 | = 0.6215, 1.15|h.sub.4         /f.sub.4 | = 0.1684                                                  f.sub.2 = 1.712, f.sub.1 = -1.115, f.sub.23 = 1.198                           f.sub.a /f.sub.b = 2.962/2.196 = 1.349, R.sub.2 = 1.9155                      R.sub.2 ' = -1.9155,  R.sub.3 = 1.3927                                        ______________________________________                                    

    ______________________________________                                        Embodiment 3                                                                  ______________________________________                                        f = 1, F.sub.No = 3.016, 2ω = 120.0°                             IH = 1.0599                                                                   ______________________________________                                        r.sub.1 = 5.3227                                                              d.sub.1 = 0.3327 n.sub.1 = 1.88300                                                                          ν.sub.1 = 40.78                              r.sub.2 = 0.7651                                                              d.sub.2 = 0.4657                                                              r.sub.3 = ∞                                                             d.sub.3 = 0.3327 n.sub.2 = 1.53172                                                                          ν.sub.2 = 48.90                              r.sub.4 = ∞                                                             d.sub.4 = 0.5089                                                              r.sub.5 = 2.3472                                                              d.sub.5 = 0.3279 n.sub.3 = 1.74100                                                                          ν.sub.3 = 52.68                              r.sub.6 = -8.0069                                                             d.sub.6 = 0.2324                                                              r.sub.7 = 8.0069                                                              d.sub.7 = 0.3279 n.sub.4 = 1.74100                                                                          ν.sub.4 = 52.68                              r.sub.8 = -2.3472                                                             d.sub.8 = 0.0665                                                              r.sub.9 = ∞ (aperture stop)                                             d.sub.9 = 0.0665                                                              r.sub.10 = 4.0786                                                             d.sub.10 = 0.5611                                                                              n.sub.5 = 1.51633                                                                          ν.sub.5 = 64.15                              r.sub.11 = -0.7418                                                            d.sub.11 = 0.3327                                                                              n.sub.6 = 1.80518                                                                          ν.sub.6 = 25.43                              r.sub.12 = -1.2948                                                            d.sub.12 = 0.4657                                                             r.sub.13 = -0.9542                                                            d.sub.13 = 0.3327                                                                              n.sub.7 = 1.72825                                                                          ν.sub.7 = 28.46                              r.sub.14 = -1.8356                                                            d.sub.14 = 0.6653                                                             r.sub.15 = ∞                                                            d.sub.15 = 0.3327                                                                              n.sub.8 = 1.51633                                                                          ν.sub.8 = 64.15                              r.sub.16 = ∞                                                            ______________________________________                                        |h.sub.1 /f.sub.1 | = 0.7424, 1.15 |h.sub.4        /f.sub.4 | = 0.1797                                                  f.sub.2 = 1.389, f.sub.1 = -1.048, f.sub.23 = 1.231                           f.sub.a /f.sub.b = 2.658/2.483 = 1.070, R.sub.2 = 2.3472                      R.sub.2 ' =  -2.3472, R.sub.3 = 4.0786                                        ______________________________________                                    

    ______________________________________                                        Embodiment 4                                                                  ______________________________________                                        f = 1, F.sub.No = 3.045, 2ω = 100.0°                             IH = 0.9126                                                                   ______________________________________                                        r.sub.1 = 3.3197                                                              d.sub.1 = 0.2583 n.sub.1 = 1.88300                                                                          ν.sub.1 = 40.78                              r.sub.2 = 0.6814                                                              d.sub.2 = 0.8784                                                              r.sub.3 = 1.8634                                                              d.sub.3 = 0.4254 n.sub.2 = 1.74100                                                                          ν.sub.2 = 52.68                              r.sub.4 = 129.9784                                                            d.sub.4 = 0.2067                                                              r.sub.5 = -61.4126                                                            d.sub.5 = 0.4274 n.sub.3 = 1.74100                                                                          ν.sub.3 = 52.68                              r.sub.6 = -1.6314                                                             d.sub.6 = 0.0572                                                              r.sub.7 = ∞ (aperture stop)                                             d.sub.7 = 0.0572                                                              r.sub.8 = 3.9424                                                              d.sub.8 = 0.6651 n.sub.4 = 1.51633                                                                          ν.sub.4 = 64.15                              r.sub.9 = -0.5959                                                             d.sub.9 = 0.2287 n.sub. 5 = 1.80518                                                                         ν.sub.5 = 25.43                              r.sub.10 = -1.1681                                                            d.sub.10 = 0.0517                                                             r.sub.11 = ∞                                                            d.sub.11 = 0.2859                                                                              n.sub.6 = 1.53172                                                                          ν.sub.6 = 48.90                              r.sub.12 = ∞                                                            d.sub.12 = 0.4031                                                             r.sub.13 = -3.1629                                                            d.sub.13 = 0.2287                                                                              n.sub.7 = 1.72825                                                                          ν.sub.7 = 28.46                              r.sub.14 = 62.5974                                                            d.sub.14 = 0.5718                                                             r.sub.15 = ∞                                                            d.sub.15 = 0.2859                                                                              n.sub.8 = 1.51633                                                                          ν.sub.8 = 64.15                              r.sub.16 =                                                                    ______________________________________                                        |h.sub.1 /f.sub.1 | = 0.6179, 1.15 |h.sub.4        /f.sub.4 | = 0.1436                                                  f.sub.2 = 1.402, f.sub.1 = -1.018, f.sub.23 = 1.248                           f.sub.a /f.sub.b = 2.840/2.255 = 1.259, R.sub.2 = 1.8634                      R.sub.2 ' = -1.6314,  R.sub.3 = 3.9424                                        ______________________________________                                    

    ______________________________________                                        Embodiment 5                                                                  ______________________________________                                        f = 1, F.sub.No = 3.021, 2ω = 119.996°                           IH = 1.0627                                                                   ______________________________________                                        r.sub.1 = 4.0027                                                              d.sub.1 = 0.3336 n.sub.1 = 1.88300                                                                          ν.sub.1 = 40.78                              r.sub.2 = 0.8672                                                              d.sub.2 = 0.5337                                                              r.sub.3 = ∞                                                             d.sub.3 = 0.3336 n.sub.2 = 1.53172                                                                          ν.sub.2 = 48.90                              r.sub.4 = ∞                                                             d.sub.4 = 0.2763                                                              r.sub.5 = 3.3266                                                              d.sub.5 = 0.3885 n.sub.3 = 1.74100                                                                          ν.sub.3 = 52.68                              r.sub.6 = -5.1676                                                             d.sub.6 = 0.2001                                                              r.sub.7 = -1.3143                                                             d.sub.7 = 0.7465 n.sub.4 = 1.74100                                                                          ν.sub.4 = 52.68                              r.sub.8 = -1.3763                                                             d.sub.8 = 0.0667                                                              r.sub.9 = ∞ (aperture stop)                                             d.sub.9 =  0.0667                                                             r.sub.10 = 1.1237                                                             d.sub.10 = 0.9237                                                                              n.sub.5 = 1.51633                                                                          ν.sub.5 = 64.15                              r.sub.11 = -0.8226                                                            d.sub.11 = 0.2668                                                                              n.sub.6 = 1.80518                                                                          ν.sub.6 = 25.43                              r.sub.12 = -1.4219                                                            d.sub.12 = 0.4003                                                             r.sub.13 = -0.8672                                                            d.sub.13 = 0.3336                                                                              n.sub.7 = 1.72825                                                                          ν.sub.7 = 28.46                              r.sub.14 = -1.8779                                                            d.sub.14 = 0.6671                                                             r.sub.15 = ∞                                                            d.sub.15 = 0.3336                                                                              n.sub.8 = 1.51633                                                                          ν.sub.8 = 64.15                              r.sub.16 = ∞                                                            ______________________________________                                        |h.sub.1 /f.sub.1 | = 0.7648, 1.15|h.sub.4         /f.sub.4 | = 0.2305                                                  f.sub.2 = 2.716, f.sub.1 = -1.320, f.sub.23 = 1.231                           f.sub.a /f.sub.b = 9.543/1.675 = 5.697, R.sub.2 = 3.327                       R.sub.2 ' =  -1.3763, R.sub.3 = 1.124                                         ______________________________________                                    

    ______________________________________                                        Embodiment 6                                                                  ______________________________________                                        f = 1, F.sub.No = 3.058, 2ω = 140.0°                             IH = 1.2009                                                                   ______________________________________                                        r.sub.1 = 6.0196                                                              d.sub.1 = 0.3762 n.sub.1 = 1.88300                                                                          ν.sub.1 = 40.78                              r.sub.2 = 1.1110                                                              d.sub.2 = 1.5577                                                              r.sub.3 = 2.6673                                                              d.sub.3 = 1.1023 n.sub.2 = 1.71736                                                                          ν.sub.2 = 29.51                              r.sub.4 = -6.2168                                                             d.sub.4 = 0.0405                                                              r.sub.5 = ∞ (aperture stop)                                             d.sub.5 = 0.1308                                                              r.sub.6 = 5.1700                                                              d.sub.6 = 0.3762 n.sub.3 = 1.69680                                                                          ν.sub.3 = 55.52                              r.sub.7 = -1745.3945                                                          d.sub.7 = 0.0967                                                              r.sub.8 = 9.8513                                                              d.sub.8 = 0.7515 n.sub.4 = 1.69680                                                                          ν.sub.4 = 55.52                              r.sub.9 = -0.7846                                                             d.sub.9 = 0.3010 n.sub.5 = 1.80518                                                                          ν.sub.5 = 25.43                              r.sub.10 = -1.2594                                                            d.sub.10 = 0.2851                                                             r.sub.11 = -1.0047                                                            d.sub.11 = 0.2591                                                                              n.sub.6 = 1.72825                                                                          ν.sub.6 = 28.46                              r.sub.12 = -1.4804                                                            d.sub.12 = 1.0030                                                             r.sub.13 = ∞                                                            d.sub.13 = 0.3762                                                                              n.sub.7 = 1.51633                                                                          ν.sub.7 = 64.15                              r.sub.14 = ∞                                                            ______________________________________                                        |h.sub.1 /f.sub.1 | = 0.7519, 1.15|h.sub.4         /f.sub.4 | = 0.1387                                                  f.sub.2 = 2.744, f.sub.1 = -1.600, f.sub.23 = 1.520                           f.sub.a /f.sub.b = 7.398/1.776 = 4.166, R.sub.2 = 2.6673                      R.sub.2 ' = -6.2168, R.sub.3 = 5.1700                                         ______________________________________                                    

    ______________________________________                                        Embodiment 7                                                                  ______________________________________                                        f = 1, F.sub.No = 2.996, 2ω = 120.82°                            IH = 1.082                                                                    ______________________________________                                        r.sub.1 = 4.3525                                                              d.sub.1 = 0.3390 n.sub.1 = 1.88300                                                                          ν.sub.1 = 40.78                              r.sub.2 = 0.7946                                                              d.sub.2 = 0.8793                                                              r.sub.3 = ∞                                                             d.sub.3 = 0.3390 n.sub.2 = 1.53172                                                                          ν.sub.2 = 48.90                              r.sub.4 = ∞                                                             d.sub.4 = 0.1627                                                              r.sub.5 = 2.5566                                                              d.sub.5 = 0.4746 n.sub.3 = 1.72825                                                                          ν.sub.3 = 28.46                              r.sub.6 = -2.5566                                                             d.sub.6 = 0.1182                                                              r.sub.7 = ∞(aperture stop)                                              d.sub.7 = 0.2585                                                              r.sub.8 = 4.6183                                                              d.sub.8 = 0.6183 n.sub.4 = 1.58913                                                                          ν.sub.4 = 60.97                              r.sub.9 = -0.8237                                                             d.sub.9 = 0.2712 n.sub. 5 = 1.80518                                                                         ν.sub.5 = 25.43                              r.sub.10 = -1.6936                                                            d.sub.10 = 0.1794                                                             r.sub.11 = 2.4014                                                             d.sub.11 = 0.4746                                                                              n.sub.6 = 1.65830                                                                          ν.sub.6 = 57.33                              r.sub.12 = -32.2502                                                           d.sub.12 = 0.2936                                                             r.sub.13 = -1.2908                                                            d.sub.13 = 0.2373                                                                              n.sub.7 = 1.80518                                                                          ν.sub.7 = 25.43                              r.sub.14 = -7.7878                                                            d.sub.14 = 0.3276                                                             r.sub.15 = ∞                                                            d.sub.15 = 0.6780                                                                              n.sub.8 = 1.54869                                                                          ν.sub.8 = 45.55                              r.sub.16 = ∞                                                            ______________________________________                                        |h.sub.1 /f.sub.1 | = 0.4766, 1.15|h.sub.4         /f.sub.4 | = 0.3672                                                  f.sub.2 = 1.827, f.sub.1 = -1.152, f.sub.23 = 1.291                           f.sub.a /f.sub.b = 3.114/1.827 = 1.869, R.sub.2 = 2.557                       R.sub.2 ' = - 2.5566, R.sub.3 = 4.618                                         ______________________________________                                    

    ______________________________________                                        Embodiment 8                                                                  ______________________________________                                        f = 1, F.sub.No = 3.007, 2ω = 140.03°                            IH = 1.1433                                                                   ______________________________________                                        r.sub.1 = 5.7307                                                              d.sub.1 = 0.3582 n.sub.1 = 1.88300                                                                          ν.sub.1 = 40.78                              r.sub.2 = 0.9213                                                              d.sub.2 = 1.5140                                                              r.sub.3 = 3.4686                                                              d.sub.3 = 0.4510 n.sub.2 = 1.72342                                                                          ν.sub.2 = 37.95                              r.sub.4 = -2.7135                                                             d.sub.4 = 0.4225                                                              r.sub.5 = ∞ (aperture stop)                                             d.sub.5 = 0.0335                                                              r.sub.6 = -1.9941                                                             d.sub.6 = 0.2149 n.sub.3 = 1.64769                                                                          ν.sub.3 = 33.80                              r.sub.7 = 10.3571                                                             d.sub.7 = 0.5806 n.sub.4 = 1.78590                                                                          ν.sub.4 = 44.18                              r.sub.8 = -2.3442                                                             d.sub.8 = 0.0116                                                              r.sub.9 = 2.4393                                                              d.sub.9 = 0.7777 n.sub. 5 = 1.69680                                                                         ν.sub.5 = 55.52                              r.sub.10 = -4.4832                                                            d.sub.10 = 0.4755                                                             r.sub.11 = -1.1857                                                            d.sub.11 = 0.3582                                                                              n.sub.6 = 1.72825                                                                          ν.sub.6 = 28.46                              r.sub.12 = -1.8661                                                            d.sub.12 = 0.9316                                                             r.sub.13 = ∞                                                            d.sub.13 = 0.3582                                                                              n.sub.7 = 1.51633                                                                          ν.sub.7 = 64.15                              r.sub.14 = ∞                                                            ______________________________________                                        |h.sub.1 /f.sub.1 | = 0.8187, 1.15|h.sub.4         /f.sub.4 | = 0.1215                                                  f.sub.2 = 2.171, f.sub.1 = -1.288, f.sub.23 = 1.482                           f.sub.a /f.sub.b = 13.805/2.171 = 6.359, R.sub.2 = 3.4686                     R.sub.2 ' = -2.7135, R.sub.3 = -1.9941                                        ______________________________________                                    

    ______________________________________                                        Embodiment 9                                                                  ______________________________________                                        f = 1, F.sub.No = 3.109, 2ω = 138.27°                            IH = 1.1424                                                                   ______________________________________                                        r.sub.1 = 5.7266                                                              d.sub.1 = 0.3579 n.sub.1 = 1.88300                                                                          ν.sub.1 = 40.78                              r.sub.2 = 0.8615                                                              d.sub.2 = 1.6801                                                              r.sub.3 = 1.7123                                                              d.sub.3 = 0.8102 n.sub.2 = 1.71300                                                                          ν.sub.2 = 53.84                              r.sub.4 = -3.5156                                                             d.sub.4 = 0.0039                                                              r.sub.5 = ∞ (aperture stop)                                             d.sub.5 = 0.0659                                                              r.sub.6 = 2.4711                                                              d.sub.6 = 0.6563 n.sub.3 = 1.51633                                                                          ν.sub.3 = 64.15                              r.sub.7 = -0.7133                                                             d.sub.7 = 0.2863 n.sub.4 = 1.80518                                                                          ν.sub.4 = 25.43                              r.sub.8 = -1.2246                                                             d.sub.8 = 0.0636                                                              r.sub.9 = ∞                                                             d.sub.9 = 0.1034 n.sub.5 = 1.53172                                                                          ν.sub.5 = 48.90                              r.sub.10 = ∞                                                            d.sub.10 = 0.1720                                                             r.sub.11 = -0.9620                                                            d.sub.11 = 0.2147                                                                              n.sub.6 = 1.72825                                                                          ν.sub.6 = 28.46                              r.sub.12 = -2.5078                                                            d.sub.12 = 0.0517                                                             r.sub.13 = 7.1019                                                             d.sub.13 = 0.5011                                                                              n.sub.7 = 1.51633                                                                          ν.sub.7 = 64.15                              r.sub.14 = -19.3899                                                           d.sub.14 = 0.7158                                                             r.sub.15 = ∞                                                            d.sub.15 = 0.3579                                                                              n.sub.8 = 1.51633                                                                          ν.sub.8 = 64.15                              r.sub.16 = ∞                                                            ______________________________________                                        |h.sub.1 /f.sub.1 | = 0.8129, 1.15|h.sub.4         /f.sub.4 | = 0.2031                                                  f.sub.2 = 1.726, f.sub.1 = -1.189, f.sub.23  = 1.262                          f.sub.a /f.sub.b = 10.132/1.726 = 5.870, R.sub.2 = 1.712                      R.sub.2 ' =  -3.5156, R.sub.3 = 2.471                                         ______________________________________                                    

    ______________________________________                                        Embodiment 10                                                                 ______________________________________                                        f = 1, F.sub.No = 3.085, 2ω = 139.536°                           IH = 1.2073                                                                   ______________________________________                                        r.sub.1 = 3.1833                                                              d.sub.1 = 0.3782 n.sub.1 = 1.88300                                                                          ν.sub.1 = 40.78                              r.sub.2 = 0.8334                                                              d.sub.2 = 1.7146                                                              r.sub.3 = 2.4300                                                              d.sub.3 = 0.7182 n.sub.2 = 1.71300                                                                          ν.sub.2 = 53.84                              r.sub.4 = -2.2325                                                             d.sub.4 = 0.0250                                                              r.sub.5 = ∞ (aperture stop)                                             d.sub.5 = 0.0546                                                              r.sub.6 = 7.1362                                                              d.sub.6 = 0.5463 n.sub.3 = 1.51633                                                                          ν.sub.3 = 64.15                              r.sub.7 = -0.7591                                                             d.sub.7 = 0.2185 n.sub.4 = 1.80518                                                                          ν.sub.4 = 25.43                              r.sub.8 = -1.2930                                                             d.sub.8 = 0.0672                                                              r.sub.9 = ∞                                                             d.sub.9 = 0.1092 n.sub.5 = 1.53172                                                                          ν.sub.5 = 48.90                              r.sub.10 = = ∞                                                          d.sub.10 = 0.3020                                                             r.sub.11 = -0.8880                                                            d.sub.11 = 0.2731                                                                              n.sub.6 = 1.72825                                                                          ν.sub.6 = 28.46                              r.sub.12 = -1.1927                                                            d.sub.12 = 0.0546                                                             r.sub.13 = 10.5247                                                            d.sub.13 = 0.5295                                                                              n.sub.7 = 1.51633                                                                          ν.sub.7 = 64.15                              r.sub.14 = 117.0536                                                           d.sub.14 = 0.7564                                                             r.sub.15 = ∞                                                            d.sub.15 = 0.3782                                                                              n.sub.8 = 1.51633                                                                          ν.sub.8 = 64.15                              r.sub.16 = ∞                                                            ______________________________________                                        |h.sub.1 /f.sub.1 | = 0.8008, 1.15 |h.sub.4        /f.sub.4 | = 0.0561                                                  f.sub.2 = 1.744, f.sub.1 = -1.383, f.sub.23 = 1.335                           f.sub.a /f.sub.b = 22.360/1.744 = 12.821, R.sub.2 = 2.430                     R.sub.2 '  = -2.2325, R.sub.3 = 7.136                                         ______________________________________                                    

    ______________________________________                                        Embodiment 11                                                                 ______________________________________                                        f = 1, F.sub.No = 3.044, 2ω = 140.082°                           IH = 1.0969                                                                   ______________________________________                                        r.sub.1 = 5.4983                                                              d.sub.1 = 0.3436 n.sub.1 = 1.88300                                                                          ν.sub.1 = 40.78                              r.sub.2 = 0.8851                                                              d.sub.2 = 1.3387                                                              r.sub.3 = 3.1007                                                              d.sub.3 = 0.4124 n.sub.2 = 1.72342                                                                          ν.sub.2 = 37.95                              r.sub.4 = -6.9867                                                             d.sub.4 = 0.2456                                                              r.sub.5 = 6.4144                                                              d.sub.5 = 0.2062 n.sub.3 = 1.69680                                                                          ν.sub.3 = 55.52                              r.sub.6 = 2.4882                                                              d.sub.6 = 0.2368                                                              r.sub.7 = ∞ (aperture stop)                                             d.sub.7 = 0.0860                                                              r.sub.8 = 3.4511                                                              d.sub.8 = 0.8753 n.sub.4 = 1.65830                                                                          ν.sub.4 = 57.33                              r.sub.9 = -2.8298                                                             d.sub.9 = 0.0932                                                              r.sub.10 = 2.2130                                                             d.sub.10 = 0.7745                                                                              n.sub.5 = 1.69680                                                                          ν.sub.5 = 55.52                              r.sub.11 = -6.8452                                                            d.sub.11 = 0.4152                                                             r.sub.12 = -1.5863                                                            d.sub.12 = 0.3436                                                                              n.sub.6 = 1.72825                                                                          ν.sub.6 = 28.46                              r.sub.13 = -5.3578                                                            d.sub.13 = 0.8408                                                             r.sub.14 = ∞                                                            d.sub.14 = 0.3436                                                                              n.sub.7 = 1.51633                                                                          ν.sub.7 = 64.15                              r.sub.15 = ∞                                                            ______________________________________                                        |h.sub.1 /f.sub.1 | = 0.8288, 1.15|h.sub.4         /f.sub.4 | = 0.2126                                                  f.sub.2 = 5.060, f.sub.1 = -1.238, f.sub.23 = 1.513                           f.sub.a /f.sub.b = 3.020/2.487 = 1.214, R.sub.2 = 3.1007                      R.sub.2 ' = 2.4882, R.sub.3 = 3.4511                                          ______________________________________                                    

    ______________________________________                                        Embodiment 12                                                                 ______________________________________                                        f = 1, F.sub.No = 3.027, 2ω = 132.72°                            IH = 1.1757                                                                   ______________________________________                                        r.sub.1 = 5.1635                                                              d.sub.1 = 0.3690 n.sub.1 = 1.88300                                                                          ν.sub.1 = 40.78                              r.sub.2 = 0.9388                                                              d.sub.2 = 0.6126                                                              r.sub.3 = 3.8306                                                              d.sub.3 = 0.2583 n.sub.2 = 1.77250                                                                          ν.sub.2 = 49.66                              r.sub.4 = 2.2149                                                              d.sub.4 = 0.9078                                                              r.sub.5 = 2.8179                                                              d.sub.5 = 0.5166 n.sub.3 = 1.72825                                                                          ν.sub.3 = 28.46                              r.sub.6 = -2.8179                                                             d.sub.6 = 0.0590                                                              r.sub.7 = ∞ (aperture stop)                                             d.sub.7 = 0.3247                                                              r.sub.8 = 4.9768                                                              d.sub.8 = 0.8119 n.sub.4 = 1.58913                                                                          ν.sub.4 = 60.97                              r.sub.9 = -0.8827                                                             d.sub.9 = 0.2952 n.sub.5 = 1.80518                                                                          ν.sub.5 = 25.43                              r.sub.10 = -2.0002                                                            d.sub.10 = 0.0738                                                             r.sub.11 = ∞                                                            d.sub.11 = 0.3690                                                                              n.sub.6 = 1.53172                                                                          ν.sub.6 = 48.90                              r.sub.12 = ∞                                                            d.sub.12 = 0.0738                                                             r.sub.13 = 3.0482                                                             r.sub.13 = 0.6274                                                                              n.sub.7 = 1.65160                                                                          ν.sub.7 = 58.52                              r.sub.14 = -5.5591                                                            d.sub.14 = 0.3026                                                             r.sub.15 = -1.5381                                                            d.sub.15 = 0.2214                                                                              n.sub.8 = 1.84666                                                                          ν.sub.8 = 23.78                              r.sub.16 = -11.0629                                                           d.sub.16 = 0.3247                                                             r.sub.17 = ∞                                                            d.sub.17 = 0.7381                                                                              n.sub.9 = 1.54869                                                                          ν.sub.9 = 45.55                              r.sub.18 = ∞                                                            ______________________________________                                        |h.sub.1 /f.sub.1 | = 0.7425, 1.15|h.sub.4         /f.sub.4 | = 0.3957                                                  f.sub.2 =  2.012, f.sub.1 = -1.031, f.sub.23 = 1.588                          f.sub.a /f.sub.b = 3.650/2.012 = 1.814, R.sub.2 = 2.8179                      R.sub.2 ' = -2.8179, R.sub.3 = 4.9768                                         ______________________________________                                    

    ______________________________________                                        Embodiment 13                                                                 ______________________________________                                        f = 1, F.sub.No = 3.012 2ω = 140.0°                              IH = 1.197                                                                    ______________________________________                                        r.sub.1 = 5.9912                                                              d.sub.1 = 0.3750 n.sub.1 = 1.88300                                                                         ν.sub.1 = 40.78                               r.sub.2 = 0.9537                                                              d.sub.2 = 0.5250                                                              r.sub.3 = 3.7795                                                              d.sub.3 = 0.2250 n.sub.2 = 1.88300                                                                         ν.sub.2 = 40.78                               r.sub.4 = 2.2136                                                              d.sub.4 = 1.1585                                                              r.sub.5 = 2.5094                                                              d.sub.5 = 0.4591 n.sub.3 = 1.72825                                                                         ν.sub.3 = 28.46                               r.sub.6 = -3.7450                                                             d.sub.6 = 0.1125                                                              r.sub.7 = ∞ (aperture stop)                                             d.sub.7 = 0.3134                                                              r.sub.8 = 4.7584                                                              d.sub.8 = 0.7459 n.sub.4 = 1.58913                                                                         ν.sub.4 = 60.97                               r.sub.9 = -0.8785                                                             d.sub.9 =  0.3000                                                                              n.sub.5 = 1.80518                                                                         ν.sub.5 = 25.43                               r.sub.10 = -2.0123                                                            d.sub.10 = 0.4069                                                             r.sub.11 = 5.0897                                                             d.sub.11 = 0.5250                                                                              n.sub.6 = 1.65830                                                                         ν.sub.6 = 57.33                               r.sub.12 = -4.6412                                                            d.sub.12 = 0.3298                                                             r.sub.13 = -1.4135                                                            d.sub.13 = 0.2250                                                                              n.sub.7 = 1.80518                                                                         ν.sub.7 = 25.43                               r.sub.14 = -3.4758                                                            d.sub.14 = 0.0088                                                             r.sub.15 = ∞                                                            d.sub.15 = 0.0750                                                                              n.sub.8 = 1.51633                                                                         ν.sub.8 = 64.15                               r.sub.16 = ∞                                                            d.sub.16 = 0.7500                                                             r.sub.17 = ∞                                                            d.sub.17 = 0.3750                                                                              n.sub.9 = 1.51633                                                                         ν.sub.9 = 64.15                               r.sub.18 = ∞                                                            ______________________________________                                        |h.sub.1 /f.sub.1 | = 0.8141, 1.15|h.sub.4         /f.sub.4 | = 0.2636                                                  f.sub.2 = 2.129, f.sub.1 = -1.002, f.sub.23 = 1.636                           f.sub.a /f.sub.b = 3.768/2.129 = 1.770, R.sub.2 = 1.5094                      R.sub.2 ' = -3.7450, R.sub.3 = 4.7584                                         ______________________________________                                    

    ______________________________________                                        Embodiment 14                                                                 ______________________________________                                        f = 1, F.sub.No = 3.001, 2ω = 120.832°                           IH = 1.2267                                                                   ______________________________________                                        r.sub.1 = 5.9125 (aspherical surface)                                         d.sub.1 = 0.3843   n.sub.1 = 1.88300                                                                         ν.sub.1 = 40.78                             r.sub.2 = 0.8298                                                              d.sub.2 = 0.9897                                                              r.sub.3 = ∞                                                             d.sub.3 = 0.3843   n.sub.2 = 1.53172                                                                         ν.sub.2 = 48.90                             r.sub.4 = ∞                                                             d.sub.4 = 0.1845                                                              r.sub.5 = 2.9048                                                              d.sub.5 = 0.5380   n.sub.3 = 1.72825                                                                         ν.sub.3 = 28.46                             r.sub.6 = -2.9283                                                             d.sub.6 = 0.1313                                                              r.sub.7 = ∞ (aperture stop)                                             d.sub.7 = 0.2910                                                              r.sub.8 = 5.4055                                                              d.sub.8 = 0.7010   n.sub.4 = 1.58913                                                                         ν.sub.4 = 60.97                             r.sub.9 =  -0.9380                                                            d.sub.9 = 0.3075   n.sub.5 = 1.80518                                                                         ν.sub.5 = 25.43                             r.sub.10 = -1.8953                                                            d.sub.10 = 0.2034                                                             r.sub.11 = 2.6198                                                             d.sub.11 = 0.5380  n.sub.6 = 1.65830                                                                         ν.sub.6 = 57.33                             r.sub.12 = -11.3821                                                           d.sub.12 = 0.3328                                                             r.sub.13 = -1.2309 (aspherical surface)                                       d.sub.13 = 0.2690  n.sub.7 = 1.80518                                                                         ν.sub.7 = 25.43                             r.sub.14 = -3.6160                                                            d.sub.14 = 0.3714                                                             r.sub.15 = ∞                                                            d.sub.15 = 0.7686  n.sub.8 = 1.54869                                                                         ν.sub.8 = 45.55                             r.sub.16 = ∞                                                            ______________________________________                                        |h.sub.1 /f.sub.1 | = 0.8266, 1.15|h.sub.4         /f.sub.4 | = 0.3411                                                  f.sub.2 = 2.083, f.sub.1 = -1.133, f.sub.23 = 1.452                           f.sub.a /f.sub.b = 3.285/2.083 = 1.577,  R.sub.2 = 2.9048                     R.sub.2 ' = -2.9283, R.sub.3 = 5.4055                                         Coefficients of aspherical surfaces                                           (1st lens surface)                                                                           P = 1, E = 0.22631 × 10.sup.-1                           (13th lens surface)                                                                          P = 1                                                          ______________________________________                                    

    ______________________________________                                        Embodiment 15                                                                 ______________________________________                                        f = 1, F.sub.No = 3.004, 2ω = 120.07°                            IH = 2.4366                                                                   ______________________________________                                        r.sub.1 = 6.3333 (aspherical surface)                                         d.sub.1 = 0.3818   n.sub.1 = 1.88300                                                                         ν.sub.1 = 40.78                             r.sub.2 = 0.8893 (aspherical surface)                                         d.sub.2 = 1.8084                                                              r.sub.3 = 1.8590                                                              d.sub.3 = 0.9825   n.sub.2 = 1.71300                                                                         ν.sub.2 = 53.84                             r.sub.4 = -3.8279                                                             d.sub.4 = 0.0042                                                              r.sub.5 = ∞ (aperture stop)                                             d.sub.5 = 0.0767                                                              r.sub.6 = 2.7250                                                              d.sub.6 = 0.7392   n.sub.3 = 1.51633                                                                         ν.sub.3 = 64.15                             r.sub.7 = -0.7605                                                             d.sub.7 = 0.3054   n.sub.4 = 1.80518                                                                         ν.sub.4 = 25.43                             r.sub.8 = -1.3061                                                             d.sub.8 =  0.3156                                                             r.sub.9 = -1.0055                                                             d.sub.9 = 0.2290   n.sub.5 = 1.72825                                                                         ν.sub.5 = 28.46                             r.sub.10 = -2.2630                                                            d.sub.10 = 0.0552                                                             r.sub.11 = 7.1359                                                             d.sub.11 = 0.5346  n.sub.6 = 1.51633                                                                         ν.sub.6 = 64.15                             r.sub.12 = -8.5566 (aspherical surface)                                       d.sub.12 = 0.7636                                                             r.sub.13 = ∞                                                            d.sub.13 = 0.3818  n.sub.7 = 1.51633                                                                         ν.sub.7 = 64.15                             r.sub.14 = ∞                                                            ______________________________________                                        |h.sub.1 /f.sub.1 | = 0.9051, 1.15|h.sub.4         /f.sub.4 | = 0.1536                                                  f.sub.2 = 1.891, f.sub.1 = -1.212, f.sub.23 = 1.404                           f.sub.a /f.sub.b = 7.624/1.891 = 4.032, R.sub.2 = 1.8590                      R.sub.2 ' = -3.8279, R.sub.3 = 2.7250                                         (Coefficients of aspherical surfaces)                                          (1st lens surface)                                                                          P = 0, E = 0.15726 × 10.sup.-1                           (2nd lens surface)                                                                           P = 1,                                                         (12th lens surface)                                                                          P = 1                                                          ______________________________________                                    

    ______________________________________                                        Embodiment 16                                                                 ______________________________________                                        f = 1, N.sub.No = 2.998,  2ω = 120.796°                          IH = 1.2469                                                                   ______________________________________                                        r.sub.1 = 5.9663 (aspherical surface)                                         d.sub.1 = 0.3906                                                                             n.sub.1 = 1.88300                                                                          ν.sub.1 = 40.78                                r.sub.2 = 0.8272                                                              d.sub.2 = 1.0070                                                              r.sub.3 = ∞                                                             d.sub.3 = 0.3906                                                                             n.sub.2 = 1.53172                                                                          ν.sub.2 = 48.90                                r.sub.4 = ∞                                                             d.sub.4 = 0.1875                                                              r.sub.5 = 3.0194                                                              d.sub.5 = 0.5469                                                                             n.sub.3 = 1.72825                                                                          ν.sub.3 = 28.46                                r.sub.6 = -2.9267                                                             d.sub.6 = 0.1334                                                              r.sub.7 = ∞ (aperture stop)                                             d.sub.7 = 0.2955                                                              r.sub.8 = 5.6257                                                              d.sub.8 = 0.7125                                                                             n.sub.4 = 1.58913                                                                          ν.sub.4 = 60.97                                r.sub.9 =  -0.9698                                                            d.sub.9     0.3125                                                                           n.sub.5 = 1.80518                                                                          ν.sub.5 = 25.43                                r.sub.10 = -1.9298                                                            d.sub.10 = 0.2068                                                             r.sub.11 = 2.5655                                                             d.sub.11 = 0.5469                                                                            n.sub.6 = 1.65830                                                                          ν.sub.6 = 57.33                                r.sub.12 = -12.9642                                                           d.sub.12 = 0.3383                                                             r.sub.13 = -1.2924 (aspherical surface)                                       d.sub.13 = 0.2734                                                                            n.sub.7 = 1.80518                                                                          ν.sub.7 = 25.43                                r.sub.14 = -4.2008                                                            d.sub.14 = 0.3775                                                             r.sub.15 = ∞                                                            d.sub.15 = 0.7813                                                                            n.sub.8 = 1.54869                                                                          ν.sub.8 = 45.55                                r.sub.16 = ∞                                                            ______________________________________                                        |h.sub.1 /f.sub.1 | = 0.8444, 1.15|h.sub.4         /f.sub.4 | = 0.3481                                                  f.sub.2 = 2.123, f.sub.1 = -1.128, f.sub.23 = 1.469                           f.sub.a /f.sub.b = 3.358/2.123 = 1.582, R.sub. 2 = 3.0194                     R.sub.2 ' = -2.9267, R.sub.3 = 5.6257                                         (coefficients of aspherical surfaces)                                         (1st lens surface)                                                                           P = 1, E = 0.24015 × 10.sup.-1                           (13th lens surface)                                                                          P = 1, E = -0.12297 × 10.sup.-1                           ##STR1##                                                                     ______________________________________                                    

    ______________________________________                                        Embodiment 17                                                                 ______________________________________                                        f = 1, F.sub.No = 3.030, 2ω = 99.99°                             IH = 1.1466                                                                   ______________________________________                                        r.sub.1 = 6.0105                                                              d.sub.1 = 0.3592                                                                             n.sub.1 = 1.88300                                                                          ν.sub.1 = 40.78                                r.sub.2 = 0.8194 (aspherical surface)                                         d.sub.2 = 0.7184                                                              r.sub.3 = 9.2577                                                              d.sub.3 = 0.3592                                                                             n.sub.2 = 1.53172                                                                          ν.sub.2 = 48.90                                r.sub.4 = -30.2947                                                            d.sub.4 = 0.3879                                                              r.sub.5 = 2.6624                                                              d.sub.5 = 0.5029                                                                             n.sub.3 = 1.72825                                                                          ν.sub.3 = 28.46                                r.sub.6 = -3.7679                                                             d.sub.6 = 0.1252                                                              r.sub.7 = ∞ (aperture stop)                                             d.sub.7 = 0.2740                                                              r.sub.8 = 4.8937                                                              d.sub.8 = 0.6552                                                                             n.sub.4 = 1.58913                                                                          ν.sub.4 = 60.97                                r.sub.9 = -0.8923                                                             d.sub.9 = 0.2874                                                                             n.sub.5 = 1.80518                                                                          ν.sub.5 = 25.43                                r.sub.10 = -1.5847                                                            d.sub.10 = 0.1901                                                             r.sub.11 = 2.5445                                                             d.sub.11 = 0.5029                                                                            n.sub.6 = 1.65830                                                                          ν.sub.6 = 57.33                                r.sub.12 = -34.1731                                                           d.sub.12 = 0.3000                                                             r.sub.13 = -1.3263                                                            d.sub.13 = 0.2514                                                                            n.sub.7 = 1.80518                                                                          ν.sub.7 = 25.43                                r.sub.14 = -7.5450 (aspherical surface)                                       d.sub.14 = 0.3471                                                             r.sub.15 = ∞                                                            d.sub.15 = 0.7184                                                                            n.sub.8 = 1.54869                                                                          ν.sub.8 = 45.55                                r.sub.16 = ∞                                                            ______________________________________                                        |h.sub.1 /f.sub.1 | = 0.4335, 1.15|h.sub.4         /f.sub.4 | = 0.3286                                                  f.sub.2 = 1.989, f.sub.1 = -1.110, f.sub.23 = 1.406                           f.sub.a /f.sub.b = 13.378/2.215 = 6.048,  R.sub.2 = 9.2577                    R.sub.2 ' = -3.7679, R.sub.3 = 4.894                                          coefficients of aspherical surfaces                                           (2nd lens surface)                                                                           P = 0, E = 0.51666 × 10.sup.-1                                          F = 0.13710                                                    (14th lens surface)                                                                          P = 0, E = 0.17323                                              ##STR2##                                                                     ______________________________________                                    

    ______________________________________                                        Embodiment 18                                                                 ______________________________________                                        f = 1, F.sub.No = 3.008, 2ω = 129.582°                           IH = 1.2449                                                                   ______________________________________                                        r.sub.1 = 7.0922 (aspherical surface)                                         d.sub.1 = 0.3901                                                                             n.sub.1 = 1.88300                                                                          ν.sub.1 = 40.78                                r.sub.2 = 0.9320 (aspherical surface)                                         d.sub.2 = 1.8376                                                              r.sub.3 = 1.9116                                                              d.sub.3 = 0.9886                                                                             n.sub.2 = 1.71300                                                                          ν.sub.2 = 53.84                                r.sub.4 = -3.8101                                                             d.sub.4 = 0.0043                                                              r.sub.5 = ∞ (aperture stop)                                             d.sub.5 = 0.0800                                                              r.sub.6 = 2.9288                                                              d.sub.6 = 0.7605                                                                             n.sub.3 = 1.51633                                                                          ν.sub.3 = 64.15                                r.sub.7 = -0.7899                                                             d.sub.7 = 0.3121                                                                             n.sub.4 = 1.80518                                                                          ν.sub.4 = 25.43                                r.sub.8 = -1.3346                                                             d.sub.8 =  0.3051                                                             r.sub.9 = -1.0142                                                             d.sub.9 = 0.2340                                                                             n.sub.5 = 1.72825                                                                          ν.sub.5 = 28.46                                r.sub.10 = -2.2485                                                            d.sub.10 = 0.0564                                                             r.sub.11 = 6.3079                                                             d.sub.11 = 0.5462                                                                            n.sub.6 = 1.51633                                                                          ν.sub.6 = 64.15                                r.sub.12 = -6.2050 (aspherical surface)                                       d.sub.12 = 0.7803                                                             r.sub.13 = ∞                                                            d.sub.13 = 0.3901                                                                            n.sub.7 = 1.51633                                                                          ν.sub.7 = 64.15                                r.sub.14 = ∞                                                            ______________________________________                                        |h.sub.1 /f.sub.1 | = 0.8950, 1.15|h.sub.4         /f.sub.4 | = 0.1226                                                  f.sub.2 = 1.924, f.sub.1 = -1.252 f.sub.23 = 1.435                            f.sub.a /f.sub.b = 6.150/1.924 = 3.196, R.sub.2 = 1.9116                      R.sub.2 ' = -3.8101, R.sub.3 = 2.9288                                         coefficients of aspherical surfaces                                           (1st lens surface)                                                                           P = 0, E = 0.12860 × 10.sup.-1                           (2nd lens surface)                                                                           P = 1                                                          (12th lens surface)                                                                          P = 1, E = 0.29866 × 10.sup.-1                            ##STR3##                                                                     ______________________________________                                    

    ______________________________________                                        Embodiment 19                                                                 ______________________________________                                        f = 1, F.sub.No = 2.996, 2ω = 110.0°                             IH = 1.2040                                                                   ______________________________________                                        r.sub.1 = 3.9397 (aspherical surface)                                         d.sub.1 = 0.3772                                                                             n.sub.1 = 1.88300                                                                          ν.sub.1 = 40.78                                r.sub.2 = 0.7949                                                              d.sub.2 = 0.6186                                                              r.sub.3 = 6.9234                                                              d.sub.3 = 0.2640                                                                             n.sub.2 = 1.77250                                                                          ν.sub.2 = 49/66                                r.sub.4 = 4.1093                                                              d.sub.4 = 0.9559                                                              r.sub.5 = 2.7606                                                              d.sub.5 = 0.5281                                                                             n.sub.3 = 1.72825                                                                          ν.sub.3 = 28.46                                r.sub.6 = -2.2016                                                             d.sub.6 = 0.0754                                                              r.sub.7 = (aperture stop)                                                     d.sub.7 = 0.3167                                                              r.sub.8 = 17.2715                                                             d.sub.8 = 0.8298                                                                             n.sub.4 = 1.58913                                                                          ν.sub.4 = 60.97                                r.sub.9 = -0.8495                                                             d.sub.9  = 0.3018                                                                            n.sub.5 = 1.80518                                                                          ν.sub.5 = 25.43                                r.sub.10 = -2.4692                                                            d.sub.10 = 0.0754                                                             r.sub.11 = ∞                                                            d.sub.11 = 0.3772                                                                            n.sub.6 = 1.53172                                                                          ν.sub.6 = 48.90                                r.sub.12 = ∞                                                            d.sub.12 = 0.0754                                                             r.sub.13 = 2.1704                                                             d.sub.13 = 0.6312                                                                            n.sub.7 = 1.65160                                                                          ν.sub.7 = 58.52                                r.sub.14 = -23.8501                                                           d.sub.14 = 0.3103                                                             r.sub.15 = -1.5651                                                            d.sub.15 = 0.2263                                                                            n.sub.8 = 1.84666                                                                          ν.sub.8 = 23.78                                r.sub.16 = -5.0483 (aspherical surface)                                       d.sub.16 = 0.3163                                                             r.sub.17 = ∞                                                            d.sub.17 = 0.7544                                                                            n.sub.9 = 1.54869                                                                          ν.sub.9 = 45.55                                r.sub.18 = ∞                                                            ______________________________________                                        |h.sub.1 /f.sub.1 | = 0.7355, 1.15|h.sub. 4        /f.sub.4 | = 0.3202                                                  f.sub.2 = 1.761. f.sub.1 = -1.033, f.sub.23 = 1.642                           f.sub.a /f.sub.b = 8.594/1.761 = 4.880 R.sub.2 = 2.7606                       R.sub.2 ' = -2.2016, R.sub.3 = 17.2715                                        coefficients of aspherical surfaces                                           (1st lens surface)                                                                           P = 1, E = 0.25038 × 10.sup.-1                                          F = 0.45776 × 10.sup.-2                                  (16th lens surface)                                                                          P = 1, E = 0.23705 × 10.sup.-1                            ##STR4##                                                                     ______________________________________                                    

    ______________________________________                                        Embodiment 20                                                                 ______________________________________                                        f = 1, F.sub.No = 3.035, 2ω = 140.02°                            IH = 1.6295                                                                   ______________________________________                                        r.sub.1 = 5.8908                                                              d.sub.1 = 0.5105   n.sub.1 = 1.88300                                                                         ν.sub.1 = 40.78                             r.sub.2 = 1.5830 (aspherical surface)                                         d.sub.2 = 2.1049                                                              r.sub.3 = 7.1003                                                              d.sub.3 = 0.7497   n.sub.2 = 1.72342                                                                         ν.sub.2 = 37.95                             r.sub.4 = -6.1767                                                             d.sub.4 = 0.0056                                                              r.sub.5 = ∞ (aperture spot)                                             d.sub.5 = 0.1188                                                              r.sub.6 = 12.6805                                                             d.sub.6 = 0.9930   n.sub.3 = 1.65830                                                                         ν.sub.3 = 57.33                             r.sub.7 = -1.2573                                                             d.sub.7 = 0.4084   n.sub.4 = 1.80518                                                                         ν.sub.4 = 25.43                             r.sub.8 = -2.0394                                                             d.sub.8 = 0.2964                                                              r.sub.9 = -1.4831                                                             d.sub.9 = 0.3063   n.sub.5 = 1.84666                                                                         ν.sub.5 = 23.78                             r.sub.10 = -1.6611                                                            d.sub.10 = 0.1532                                                             r.sub.11 = 8.1827                                                             d.sub.11 = 0.7147  n.sub.6 = 1.51633                                                                         ν.sub.6 = 64.15                             r.sub.12 = -1.8839 (aspherical surface)                                       d.sub.12 = 1.0291                                                             d.sub.13 = ∞                                                            d.sub.13 = 0.5105  n.sub.7 = 1.51633                                                                         ν.sub.7 = 64.15                             r.sub.14 = ∞                                                            ______________________________________                                        |h.sub.1 /f.sub.1 | = 0.6747, 1.15|h.sub.4         /f.sub.4 | = 0.3865                                                  f.sub.2 = 4.677, f.sub.1 = -2.596, f.sub.23 = 2.168                           f.sub.a /f.sub.b = 4.677/3.039 = 1.539, R.sub.2 = 7.01003                     R.sub.2 ' = -6.1767, R.sub.3 = 12.6805                                        coefficients of aspherical surfaces                                           (2nd lens surface)                                                                           P = 1, E = 0.59267 × 10.sup.-1                                          F = -0.29531 × 10.sup.-1                                 (12th lens surface)                                                                          P = 1, E = 0.10652                                             Q.sub.h = 1.1459                                                              ______________________________________                                    

    ______________________________________                                        Embodiment 21                                                                 ______________________________________                                        f = 1, F.sub.No = 3.032, 2ω = 140.0°                             IH = 1.4229                                                                   ______________________________________                                        r.sub.1 = 5.6068                                                              d.sub.1 = 0.4458   n.sub.1 = 1.88300                                                                         ν.sub.1 = 40.78                             r.sub.2 = 1.2801 (aspherical surface)                                         d.sub.2 = 2.0273                                                              r.sub.3 = 3.6331                                                              d.sub.3 = 0.7592   n.sub.2 = 1.72342                                                                         ν.sub.2 = 37.95                             r.sub.4 = -5.0124                                                             d.sub.4 = 0.0049                                                              r.sub.5 = ∞ (aperture stop)                                             d.sub.5 = 0.1026                                                              r.sub.6 = 7.4259                                                              d.sub.6 = 0.8539   n.sub.3 = 1.65830                                                                         ν.sub.3 = 57.33                             r.sub.7 = -1.1844                                                             d.sub.7 = 0.3566   n.sub.4 = 1.80518                                                                         ν.sub.4 = 25.43                             r.sub.8 = -1.7581                                                             d.sub.8 = 0.3181                                                              r.sub.9 = -1.2303                                                             d.sub.9 = 0.2675   n.sub.5 = 1.84666                                                                         ν.sub.5 = 23.78                             r.sub.10 = -1.6302                                                            d.sub.10 = 0.1337                                                             r.sub.11 = 50.6667                                                            d.sub.11 = 0.6241  n.sub.6 = 1.51633                                                                         ν.sub.6 = 64.15                             r.sub.12 = -2.1201 (aspherical surface)                                       d.sub.12 = 0.8985                                                             r.sub.13 = ∞                                                            d.sub.13 = 0.4458  n.sub.7 = 1.51633                                                                         ν.sub.7 = 64.15                             r.sub.14 = ∞                                                            ______________________________________                                        |h.sub.1 /f.sub.1 | = 0.7323, 1.15|h.sub.4         /f.sub.4 | = 0.1542                                                  f.sub.2 = 3.023, f.sub.1 = -1.974, f.sub.23 = 1.662                           f.sub.a /f.sub.b = 3.957/2.439 = 1.622, R.sub.2 = 3.6331                      R.sub.2 ' = -5.0124. R.sub.3 = 7.4259                                         Coefficients of aspherical surfaces                                           (2nd surface) P = 1, E = 0.61335 × 10.sup.-1                                          F = -0.39851 × 10.sup.-1                                  (12th surface)                                                                              P = 1, E = 0.10463                                              Q.sub.h = 1.3035                                                              ______________________________________                                    

    ______________________________________                                        Embodiments 22                                                                ______________________________________                                        f = 1, F.sub.No = 3.033, 2ω = 140.01°                            IH = 1.4387                                                                   ______________________________________                                        r.sub.1 = 4.1525                                                              d.sub.1 = 0.4507   n.sub.1 = 1.88300                                                                         ν.sub.1 = 40.78                             r.sub.2 = 1.2907 (aspherical surface)                                         d.sub.2 = 1.9824                                                              r.sub.3 = 6.0185                                                              d.sub.3 = 0.6489   n.sub.2 = 1.72342                                                                         ν.sub.2 = 37.95                             r.sub.4 = -5.3701                                                             d.sub.4 = 0.0050                                                              r.sub.5 = ∞ (aperture stop)                                             d.sub.5 = 0.0988                                                              r.sub.6 = 9.8733                                                              d.sub.6 = 0.7706   n.sub.3 = 1.65830                                                                         ν.sub.3 = 57.33                             r.sub.7 = -2.1176                                                             d.sub.7 = 0.3606   n.sub.4 = 1.80518                                                                         ν.sub.4 = 25.43                             r.sub.8 = -1.7128                                                             d.sub.8 = 0.3216                                                              r.sub.9 = -1.6356                                                             d.sub.9 = 0.2704   n.sub.5 = 1.84666                                                                         ν.sub.5 = 23.78                             r.sub.10 = -1.6634 (aspherical surface)                                       d.sub.10 = 0.1352                                                             r.sub.11 = -3.0982                                                            d.sub.11 = 0.6310  n.sub.6 = 1.51633                                                                         ν.sub.6 = 64.15                             r.sub.12 = -1.5977 (aspherical surface)                                       d.sub.12 = 0.9086                                                             r.sub.13 = ∞                                                            d.sub.13 = 0.4507  n.sub.7 = 1.51633                                                                         ν.sub.7 = 64.15                             r.sub.14 = ∞                                                            ______________________________________                                        |h.sub.1 /f.sub.1 | = 0.6803, 1.15|h.sub.4         /f.sub.4 | = 0.1969                                                  f.sub.2 = 4.019, f.sub.1 = -2.290, f.sub.23 = 1.664                           f.sub.a /f.sub.b = 33.391/2.198 = 15.192, R.sub.2 = 6.0185                    R.sub.2 ' = -5.3701, R.sub.3 = 9.8733                                         coefficients of aspherical surfaces                                           (2nd lens surface)                                                                           P = 1, E = 0.64518 × 10.sup.-1                                          F = -0.38100 × 10.sup.-1                                 (10th lens surface)                                                                          P = 1, E = 0.10921                                             (12th lens surface)                                                                          P = 1, E = 0.82721 × 10.sup.-2                           Q.sub.h = 1.3030                                                              ______________________________________                                    

In respective embodiments shown in the above, reference symbols r1, r2,. . . respectively represent radii of curvature of respective lenssurfaces, reference symbols d1, d2, . . . respectively representthicknesses of respective lenses and airspaces between respectivelenses, reference symbols n1, n2, . . . respectively representrefractive indices of respective lenses, and reference symbols v1, v2, .. . respectively represent Abbe's numbers of respective lenses. Out ofcoefficients of aspherical surface, those which are not shown in thenumerical data are zero.

Embodiments 1 through 22 shown in the above respectively have lensconfigurations as shown in FIGS. 10 through 31. Out of them, each ofEmbodiments 14 through 22 is arranged as a lens system comprisingaspherical lens components, and the coefficients of aspherical surfaceetc. are shown in the numerical data thereof. Embodiments 16 through 19respectively fulfill the condition (17), and Embodiments 20 through 22respectively fulfill the condition (22).

Besides, Embodiments 16 through 19 are respectively arranged to furtherfulfill the condition (15), and the lens systems illustrated byEmbodiments 16 through 19 are respectively arranged that both ofdistortion and curvature of field are corrected favourably.

Embodiments 14 through 22 are respectively arranged that the lens systemis provided with aspherical surfaces therein in the state that eitherthe surface on the object side of at least one of lens componentsconstituting the front subsystem located in front of the aperture stop Shas such portions whose curvature becomes gradually stronger as they arefarther from the optical axis or the surface on the image side of atleast one lens components constituting the front subsystem located infront of the aperture stop S has such portions whose curvature becomesgradually weaker as they are farther from the optical axis, or in thestate that either the surface on the object side of at least one of lenscomponents constituting the rear subsystem located in rear of theaperture stop S has such portions whose curvature becomes graduallyweaker as they are farther from the optical axis or the surface on theimage side of at least one of lens components constituting the rearsubsystem located in rear of the aperture stop S has such portions whosecurvature becomes gradually stronger as they are farther from theoptical axis, Embodiments 14 through 22 being thereby arranged that itis possible to correct distortion and curvature of field favourably.

For example, in case of the objective for an endoscope illustrated byEmbodiment 17 shown in FIG. 26, the second surface thereof is formedthat its curvature becomes gradually weaker toward its portion fartherfrom the optical axis, and the thirteenth surface thereof is formed thatits curvature becomes gradually stronger toward its position fartherfrom the optical axis.

In case of the objective for an endoscope illustrated by Embodiment 14shown in FIG. 23, the aspherical surface provided in the front subsystemis adopted for the surface on the object side of a lens componenttherein, and said aspherical surface is formed so as to at least havesuch portions whose curvature becomes gradually stronger as they arefarther from the optical axis. Besides, in case of the objective for anendoscope illustrated by Embodiment 15 shown in FIG. 24, anotheraspherical surface is adopted also for the surface on the image side ofa lens component in the front subsystem, and said aspherical surface isformed so as to at least have such portions whose curvature becomesgradually weaker as they are farther from the optical axis.

In preferred embodiments described so far, the plane-parallel plate Fwhich is located at a position between the front end of the first lensunit I and rear end of the fourth lens unit IV is a filter foreliminating the rays of such wavelengths, i.e., infrared rays, that arenot used for observation by a solid-state image pick-up device. Saidfilter may be arranged as any of an interference filter, absorptionfilter, and absorption filter provided with a coating. Said filter maybe arranged also as a member which attenuates the rays of suchwavelengths that are not used for observation, for example, a filterwhich attenuates the beam of helium-neon laser, which is used as theguide beam of YAG laser. Furthermore, the plane-parallel palte C whichis located in rear of the fourth lens unit IV is a dust-preventing glassfor the solid-state image pick-up device.

Aberration curves of preferred embodiments described so far as shown inFIGS. 32 through 53.

We claim:
 1. An objective for an endoscope comprising, in the order from the object side, a first lens having a negative refractive power, a second lens unit having positive refractive power, a third lens unit having positive refractive power, an aperture stop arranged between the front end of said second lens unit and rear end of said third lens unit, and a fourth lens unit comprising a lens component having a concave surface on the object side, said objective for an endoscope being arranged to comprise at least three positive lens components including a cemented doublet and respectively located at positions between the front end of said second lens unit and rear end of said fourth lens unit.
 2. An objective for an endoscope according to claim 1 fulfilling the condition (1) shown below:

    |h.sub.1 /f.sub.1 |>1.15|h.sub.4 /f.sub.4 |                                                (1)

where, reference symbol h₁ represents the mean value of heights of principal rays on respective surfaces of said first lens unit, reference symbol h₄ represents the mean value of heights of principal rays on respective surfaces of said fourth lens unit, reference symbol f₁ represents the focal length of said first lens unit, and reference symbol f₄ represents the focal length of said fourth lens unit.
 3. An objective for an endoscope according to claim 2 further fulfilling the condition (2) shown below:

    f.sub.2 <9f                                                (2)

where, reference symbol f₂ represents the focal length of said second lens unit, and reference symbol f represents the focal length of the lens system as a whole.
 4. An objective for an endoscope according to claim 3 further fulfilling the conditions (3), (4), (5) and (6) shown below:

    |f.sub.1 |<5f                            (3)

    |f.sub.23 |<4.5f                         (4)

    |f.sub.a /f.sub.b |<30                   (5)

    R.sub.2 >0                                                 (6)

where, reference symbol f₂₃ represents the total focal length of said second and third lens units, reference symbols f_(a) and f_(b) respectively represent the largest value and smallest value out of the focal lengths of said at least three positive lens components including a cemented doublet which are respectively arranged at positions between the front end of said second lens unit and rear end of said fourth lens unit, and reference symbol R₂ represents the radius of curvature of the foremost surface of said second lens unit.
 5. An objective for an endoscope according to claim 4 further fulfilling the conditions (7) and (8) shown below:

    -R.sub.2 '≦15f                                      (7)

    R.sub.3 ≦30f                                        (8)

where, reference symbol R₂ ' represents the radius of curvature of the rearmost surface of said second lens unit, and reference symbol R₃ represents the radius of curvature of the foremost surface o said third lens unit.
 6. An objective for an endoscope according to claim 5 having the following numerical data:

    ______________________________________                                         f = 1, F.sub.No = 3.018, 2ω = 100.926°                            IH = 0.9184                                                                    ______________________________________                                         r.sub.1 = 4.4097                                                               d.sub.1 = 0.2877 n.sub.1 = 1.88300                                                                          ν.sub.1 = 40.78                                r.sub.2 = 0.7457                                                               d.sub.2 = 1.0472                                                               r.sub.3 = 2.0242                                                               d.sub.3 = 0.3049 n.sub.2 = 1.74100                                                                          ν.sub.2 = 52.68                                r.sub.4 = ∞                                                              d.sub.4 = 0.3510                                                               r.sub.5 = ∞                                                              d.sub.5 = 0.3049 n.sub.3 = 1.74100                                                                          ν.sub.3 = 52.68                                r.sub.6 = -2.0242                                                              d.sub.6 = 0.0575                                                               r.sub.7 = ∞ (aperture stop)                                              d.sub.7 = 0.0575                                                               r.sub.8 = 1.6116                                                               d.sub.8 = 0.5696 n.sub.4 = 1.51633                                                                          ν.sub.4 = 64.15                                r.sub.9 = -1.0213                                                              d.sub.9 = 0.2301 n.sub.5 = 1.80518                                                                          ν.sub.5 = 25.43                                r.sub.10 = -2.1617                                                             d.sub.10 = 0.0575                                                              r.sub.11 = ∞                                                             d.sub.11 = 0.2877                                                                               n.sub.6 = 1.53172                                                                          ν.sub.6 = 48.90                                r.sub.12 = ∞                                                             d.sub.12 = 0.3625                                                              r.sub.13 = -0.8009                                                             d.sub.13 = 0.2301                                                                               n.sub.7 = 1.72825                                                                          ν.sub.7 = 28.46                                r.sub.14 = -1.3705                                                             d.sub.14 = 0.3855                                                              r.sub.15 = ∞                                                             d.sub.15 = 0.5754                                                                               n.sub.8 = 1.51633                                                                          ν.sub.8 = 64.15                                r.sub.16 = ∞                                                             ______________________________________                                         |h.sub.1 /f.sub.1 | = 0.6308, 1.15|h.sub.4          /f.sub.4 | = 0.1670                                                   f.sub.2 = 1.567, f.sub.1 = -1.055, f.sub.23 = 1.179                            f.sub.a /f.sub.b =  2.732/2.526 = 1.082, R.sub.2 = 2.024                       R.sub.2 ' = -2.024, R.sub.3 = 1.612                                            ______________________________________                                    

where, reference symbols r₁, r₂, . . . respectively represent radii of curvature of respective lens surfaces, reference symbols d₁, d₂, . . . respectively represent thicknesses of respective lenses and airspaces between respective lenses, reference symbols n₁, n₂, . . . respectively represent refractive indices of respective lenses, and reference symbols ν₁, ν₂, . . . respectively represent Abbe's numbers of respective lenses.
 7. An objective for an endoscope according to claim 5 having the following numerical data:

    ______________________________________                                         f = 1, F.sub.No = 3.102, 2ω= 100.03°                              IH = 0.9142                                                                    ______________________________________                                         r.sub.1 = 3.6033                                                               d.sub.1 = 0.2864 n.sub.1 = 1.88300                                                                          ν.sub.1 = 40.78                                r.sub.2 = 0.7446                                                               d.sub.2 = 1.0439                                                               r.sub.3 = 1.9155                                                               d.sub.3 = 0.3136 n.sub.2 = 1.74100                                                                          ν.sub.2 = 52.68                                r.sub.4 = 13.9967                                                              d.sub.4 = 0.3855                                                               r.sub.5 = -13.9967                                                             d.sub.5 = 0.3136 n.sub.3 = 1.74100                                                                          ν.sub.3 = 52.68                                r.sub.6 = -1.9155                                                              d.sub.6 = 0.0573                                                               r.sub.7 = ∞ (aperture stop)                                              d.sub.7 = 0.0573                                                               r.sub.8 = 1.3927                                                               d.sub.8 = 0.6192 n.sub.4 = 1.51633                                                                          ν.sub.4 = 64.15                                r.sub.9 = -0.9683                                                              d.sub.9 = 0.2291 n.sub.5 = 1.80518                                                                          ν.sub.5 = 25.43                                r.sub.10 = -1.9872                                                             d.sub.10 = 0.0573                                                              r.sub.11 = ∞                                                             d.sub.11 = 0.2864                                                                               n.sub.6 = 1.53172                                                                          ν.sub.6 = 48.90                                r.sub.12 = ∞                                                             d.sub.12 = 0.3023                                                              r.sub.13 = -0.8271                                                             d.sub.13 = 0.2291                                                                               n.sub.7 = 1.72825                                                                          ν.sub.7 = 28.46                                r.sub.14 = -1.4614                                                             d.sub.14 = 0.5727                                                              r.sub.15 = ∞                                                             d.sub.15 = 0.2864                                                                               n.sub.8 = 1.51633                                                                          ν.sub.8 = 64.15                                r.sub.16 = ∞                                                             ______________________________________                                         |h.sub.1 /f.sub.1 | = 0.6215, 1.15 |h.sub.4         /f.sub.4 | = 0.1684                                                   f.sub.2 = 1.712, f.sub.1 = -1.115, f.sub.23 = 1.198                            f.sub.a /f.sub.b = 2.962/2.196 = 1.349, R.sub.2 = 1.9155                       R.sub.2 ' = -1.9155, R.sub.3 = 1.3927                                          ______________________________________                                    

where, reference symbols r₁, r₂, . . . respectively represent radii of curvature of respective lens surfaces, reference symbols d₁, d₂, . . . respectively represent thicknesses of respective lenses and airspaces between respective lenses, reference symbols n₁, n₂, . . . respectively represent refractive indices of respective lenses, and reference symbols ν₁, ν₂, . . . respectively represent Abbe's numbers of respective lenses.
 8. An objective for an endoscope according to claim 5 having the following numerical data:

    ______________________________________                                         f = 1, F.sub.No = 3.016, 2ω = 120.0°                              IH = 1.0599                                                                    ______________________________________                                         r.sub.1 = 5.3227                                                               d.sub.1 = 0.3327 n.sub.1 = 1.88300                                                                          ν.sub.1 = 40.78                                r.sub.2 = 0.7651                                                               d.sub.2 = 0.4657                                                               r.sub.3 = ∞                                                              d.sub.3 = 0.3327 n.sub.2 = 1.53172                                                                          ν.sub.2 = 48.90                                r.sub.4 = ∞                                                              d.sub.4 = 0.5089                                                               r.sub.5 = 2.3472                                                               d.sub.5 = 0.3279 n.sub.3 = 1.74100                                                                          ν.sub.3 = 52.68                                r.sub.6 = -8.0069                                                              d.sub.6 = 0.2324                                                               r.sub.7 = 8.0069                                                               d.sub.7 = 0.3279 n.sub.4 = 1.74100                                                                          ν.sub.4 = 52.68                                r.sub.8 = -2.3472                                                              d.sub.8 = 0.0665                                                               r.sub.9 = ∞ (aperture stop)                                              d.sub.9 = 0.0665                                                               r.sub.10 =  4.0786                                                             d.sub.10 = 0.5611                                                                               n.sub.5 = 1.51633                                                                          ν.sub.5 = 64.15                                r.sub.11 = -0.7418                                                             d.sub.11 = 0.3327                                                                               n.sub.6 = 1.80518                                                                          ν.sub.6 = 25.43                                r.sub.12 = -1.2948                                                             d.sub.12 = 0.4657                                                              r.sub.13 = -0.9542                                                             d.sub.13 = 0.3327                                                                               n.sub.7 = 1.72825                                                                          ν.sub.7 = 28.46                                r.sub.14 = -1.8356                                                             d.sub.14 = 0.6653                                                              r.sub.15 = ∞                                                             d.sub.15 = 0.3327                                                                               n.sub.8 = 1.51633                                                                          ν.sub.8 = 64.15                                r.sub.16 = ∞                                                             ______________________________________                                         |h.sub.1 /f.sub.1 | = 0.7424, 1.15|h.sub.4          /f.sub.4 | = 0.1797                                                   f.sub.2 = 1.389, f.sub.1  = -1.048, f.sub.23 = 1.231                           f.sub.a /f.sub.b = 2.658/2.483 = 1.070, R.sub.2 = 2.3472                       R.sub.2 ' = -2.3472, R.sub.3  = 4.0786                                         ______________________________________                                    

where, reference symbols r₁, r₂, . . . respectively represent radii of curvature of respective lens surfaces, reference symbols d₁, d₂, . . . respectively represent thicknesses of respective lenses and airspaces between respective lenses, reference symbols n₁, n₂, . . . respectively represent refractive indices of respective lenses, and reference symbols ν₁, ν₂, . . . respectively represent Abbe's numbers of respective lenses.
 9. An objective for an endoscope according to claim 5 having the following numerical data:

    ______________________________________                                         f = 1, F.sub.No = 3.045, 2ω = 100.0°                              IH = 0.9126                                                                    ______________________________________                                         r.sub.1 = 3.3197                                                               d.sub.1 = 0.2583 n.sub.1 = 1.88300                                                                          ν.sub.1 = 40.78                                r.sub.2 = 0.6814                                                               d.sub.2 = 0.8784                                                               r.sub.3 = 1.8634                                                               d.sub.3 = 0.4254 n.sub.2 = 1.74100                                                                          ν.sub.2 = 52.68                                r.sub.4 = 129.9784                                                             d.sub.4 = 0.2067                                                               r.sub.5 = -61.4126                                                             d.sub.5 = 0.4274 n.sub.3 = 1.74100                                                                          ν.sub.3 = 52.68                                r.sub.6 = -1.6314                                                              d.sub.6 = 0.0572                                                               r.sub.7 = ∞ (aperture stop)                                              d.sub.7 = 0.0572                                                               r.sub.8 = 3.9424                                                               d.sub.8 = 0.6651 n.sub.4 = 1.51633                                                                          ν.sub.4 = 64.15                                r.sub.9 = -0.5959                                                              d.sub.9 = 0.2287 n.sub.5 =  1.80518                                                                         ν.sub.5 = 25.43                                r.sub.10 = -1.1684                                                             d.sub.10 = 0.0517                                                              r.sub.11 = ∞                                                             d.sub.11 = 0.2859                                                                               n.sub.6 = 1.53172                                                                          ν.sub.6 = 48.90                                r.sub.12 = ∞                                                             d.sub.12 = 0.4031                                                              r.sub.13 = -3.1629                                                             d.sub.13 = 0.2287                                                                               n.sub.7 = 1.72825                                                                          ν.sub.7 = 28.46                                r.sub.14 = 62.5974                                                             d.sub.14 = 0.5718                                                              r.sub.15 = ∞                                                             d.sub.15 = 0.2859                                                                               n.sub.8 = 1.51633                                                                          ν.sub.8 = 64.15                                r.sub.16 = ∞                                                             ______________________________________                                         |h.sub.1 /f.sub.1 | = 0.6179, 1.15|h.sub.4          /f.sub.4 |= 0.1436                                                    f.sub.2 = 1.402, f.sub.1 = -1.018, f.sub.23 = 1.248                            f.sub.a /f.sub.b = 2.840/2.255 = 1.259, R.sub.2 = 1.8634                       R.sub.2 ' = -1.6314, R.sub.3 =  3.9424                                         ______________________________________                                    

where, reference symbols r₁, r₂, . . . respectively represent radii of curvature of respective lens surfaces, reference symbols d₁, d₂, . . . respectively represent thicknesses of respective lenses and airspaces between respective lenses, reference symbols n₁, n₂, . . . respectively represent refractive indices of respective lenses, and reference symbols ν₁, ν₂, . . . respectively represent Abbe's number of respective lenses.
 10. An objective for an endoscope according to claim 5 having the following numerical data:

    ______________________________________                                         f = 1, F.sub.No = 3.021 2ω = 119.996°                             IH = 1.0627                                                                    ______________________________________                                         r.sub.1 = 4.0027                                                               d.sub.1 = 0.3336 n.sub.1 = 1.88300                                                                          ν.sub.1 = 40.78                                r.sub.2 = 0.8672                                                               d.sub.2 = 0.5337                                                               r.sub.3 = ∞                                                              d.sub.3 = 0.3336 n.sub.2 = 1.53172                                                                          ν.sub.2 = 48.90                                r.sub.4 = ∞                                                              d.sub.4 = 0.2763                                                               r.sub.5 = 3.3266                                                               d.sub.5 = 0.3885 n.sub.3 = 1.74100                                                                          ν.sub.3 = 52.68                                r.sub.6 = -5.1676                                                              d.sub.6 = 0.2001                                                               r.sub.7 = -1.3143                                                              d.sub.7 = 0.7465 n.sub.4 = 1.74100                                                                          ν.sub.4 = 52.68                                r.sub.8 = -1.3763                                                              d.sub.8 = 0.0667                                                               r.sub.9 = ∞ (aperture stop)                                              d.sub.9 = 0.0667                                                               r.sub.10  = 1.1237                                                             d.sub.10 = 0.9237                                                                               n.sub.5 = 1.51633                                                                          ν.sub.5 = 64.15                                r.sub.11 = -0.8226                                                             d.sub.11 = 0.2668                                                                               n.sub.6 = 1.80518                                                                          ν.sub.6 = 25.43                                r.sub.12 = -1.4219                                                             d.sub.12 = 0.4003                                                              r.sub.13 = -0.8672                                                             d.sub.13 = 0.3336                                                                               n.sub.7 = 1.72825                                                                          ν.sub.7 = 28.46                                r.sub.14 = -1.8779                                                             d.sub.14 = 0.6671                                                              r.sub.15 = ∞                                                             d.sub.15 = 0.3336                                                                               n.sub.8 = 1.51633                                                                          ν.sub.8 = 64.15                                r.sub.16 = ∞                                                             ______________________________________                                         |h.sub.1 /f.sub.1 | = 0.7648, 1.15|h.sub.4          /f.sub.4 | = 0.2305                                                   f.sub.2 = 2.716, f.sub.1 = -1.320, f.sub.23 = 1.231                            f.sub.a /f.sub.b = 9.543/1.675  = 5.697, R.sub.2 = 3.327                       R.sub.2 ' = -1.3763, R.sub. 3 = 1.124                                          ______________________________________                                    

where, reference symbols r₁, r₂, . . . respectively represent radii of curvature of respective lens surfaces, reference symbols d₁, d₂, . . . respectively represent thicknesses of respective lenses and airspaces between respective lenses, reference symbols n₁, n₂, . . . respectively represent refractive indices of respective lenses, and reference symbols ν₁, ν₂, . . . respectively represent Abbe's numbers of respective lenses.
 11. An objective for an endoscope according to claim 5 having the following numerical data:

    ______________________________________                                         f = 1, F.sub.No = 3.058 2ω = 140.0°                               IH = 1.2009                                                                    ______________________________________                                         r.sub.1 = 6.0196                                                               d.sub.1 = 0.3762 n.sub.1 = 1.88300                                                                          ν.sub.1 = 40.78                                r.sub.2 = 1.1110                                                               d.sub.2 = 1.5577                                                               r.sub.3 = 2.6673                                                               d.sub.3 = 1.1023 n.sub.2 = 1.71736                                                                          ν.sub.2 = 29.51                                r.sub.4 = -6.2168                                                              d.sub.4 = 0.0405                                                               r.sub.5 = ∞ (aperture stop)                                              d.sub.5 = 0.1308                                                               r.sub.6 = 5.1700                                                               d.sub.6 = 0.3762 n.sub.3 = 1.69680                                                                          ν.sub.3 = 55.52                                r.sub.7 = -1745.3945                                                           d.sub.7 = 0.0967                                                               r.sub.8 = 9.8513                                                               d.sub.8 = 0.7515 n.sub.4 = 1.69680                                                                          ν.sub.4 = 55.52                                r.sub.9 = -0.7846                                                              d.sub.9 = 0.3010 n.sub.5 =  1.80518                                                                         ν.sub.5 = 25.43                                r.sub.10 = -1.2594                                                             d.sub.10 = 0.2851                                                              r.sub.11 = -1.0047                                                             d.sub.11 = 0.2591                                                                               n.sub.6 = 1.72825                                                                          ν.sub.6 = 28.46                                r.sub.12 = -1.4804                                                             d.sub.12 = 1.0030                                                              r.sub.13 = ∞                                                             d.sub.13 = 0.3762                                                                               n.sub.7 = 1.51633                                                                          ν.sub.7 = 64.15                                r.sub.14 = ∞                                                             ______________________________________                                         |h.sub.1 /f.sub.1 | = 0.7519, 1.15|h.sub.4          /f.sub.4 | = 0.1387                                                   f.sub.2 = 2.744, f.sub.1 = -1.600, f.sub.23 = 1.520                            f.sub.a /f.sub.b = 7.398/1.776 = 4.166, R.sub.2 = 2.6673                       R.sub.2 ' = -6.2168, R.sub.3 = 5.1700                                          ______________________________________                                    

where, reference symbols r₁, r₂, . . . respectively represent radii of curvature of respective lens surfaces, reference symbols d₁, d₂, . . . respectively represent thicknesses of respective lenses and airspaces between respective lenses, reference symbols n₁, n₂, . . . respectively represent refractive indices of respective lenses, and reference symbols ν₁, ν₂, . . . respectively represent Abbe's numbers of respective lenses.
 12. An objective for an endoscope according to claim 5 having the following numerical data:

    ______________________________________                                         f = 1, F.sub.No = 2.996, 2ω = 120.82°                             IH = 1.082                                                                     ______________________________________                                         r.sub.1 = 4.3525                                                               d.sub.1 = 0.3390 n.sub.1 = 1.88300                                                                          ν.sub.1 = 40.78                                r.sub.2 = 0.7946                                                               d.sub.2 = 0.8793                                                               r.sub.3 = ∞                                                              d.sub.3 = 0.3390 n.sub.2 = 1.53172                                                                          ν.sub.2 = 48.90                                r.sub.4 = ∞                                                              d.sub.4 = 0.1627                                                               r.sub.5 = 2.5566                                                               d.sub.5 = 0.4746 n.sub.3 = 1.72825                                                                          ν.sub.3 = 28.46                                r.sub.6 = -2.5566                                                              d.sub.6 = 0.1182                                                               r.sub.7 = ∞ (aperture stop)                                              d.sub.7 = 0.2585                                                               r.sub.8 = 4.6183                                                               d.sub.8 = 06183  n.sub.4 = 1.58913                                                                          ν.sub.4 = 60.97                                r.sub.9 = -0.8237                                                              d.sub.9 = 0.2712 n.sub.5 = 1.80518                                                                          ν.sub. 5 = 25.43                               r.sub.10 = -1.6936                                                             d.sub.10 = 0.1794                                                              r.sub.11 = 2.4014                                                              d.sub.11 = 0.4746                                                                               n.sub.6 = 1.65830                                                                          ν.sub.6 = 57.33                                r.sub.12 = -32.2502                                                            d.sub.12 = 0.2936                                                              r.sub.13 = -1.2908                                                             d.sub.13 = 0.2373                                                                               n.sub.7 = 1.80518                                                                          ν.sub.7 = 25.43                                r.sub.14 = -7.7878                                                             d.sub.14 = 0.3276                                                              r.sub.15 = ∞                                                             d.sub.15 = 0.6780                                                                               n.sub.8 = 1.54869                                                                          ν.sub.8 = 45.55                                r.sub.16 = ∞                                                             ______________________________________                                         |h.sub.1 /f.sub.1 | = 0.4766, 1.15 |h.sub.4         /f.sub.4 | = 0.3672                                                   f.sub.2 = 1.827, f.sub.1 = -1.152, f.sub.23 = 1.291                            f.sub.a /f.sub.b = 3.414/1.827 = 1.869, R.sub.2 = 2.557                        R.sub.2 ' = -2.5566, R.sub.3 = 4.168                                           ______________________________________                                    

where, reference symbols r₁, r₂, . . . respectively represent radii of curvature of respective lens surfaces, reference symbols d₁, d₂, . . . respectively represent thicknesses of respective lenses and airspaces between respective lenses, reference symbols n₁, n₂, . . . respectively represent refractive indices of respective lenses, and reference symbols ν₁, ν₂, . . . respectively represent Abbe's numbers of respective lenses.
 13. An objective for an endoscope according to claim 5 having the following numerical data:

    ______________________________________                                         f = 1, f.sub.No = 3.007 2ω = 140.03°                              IH = 1.1433                                                                    ______________________________________                                         r.sub.1 = 5.7307                                                               d.sub.1 = 0.3582 n.sub.1 = 1.88300                                                                          ν.sub.1 = 40.78                                r.sub.2 = 0.9213                                                               d.sub.2 = 1.5140                                                               r.sub.3 = 3.4686                                                               d.sub.3 = 0.4510 n.sub.2 = 1.72342                                                                          ν.sub.2 = 37.95                                r.sub.4 = -2.7135                                                              d.sub.4 = 0.4225                                                               r.sub.5 = ∞ (aperture stop)                                              d.sub.5 = 0.0335                                                               r.sub.6 = -1.9941                                                              d.sub.6 = 0.2149 n.sub.3 = 1.64769                                                                          ν.sub.3 = 33.80                                r.sub.7 = 10.3571                                                              d.sub.7 = 0.5806 n.sub.4 = 1.78590                                                                          ν.sub.4 = 44.18                                r.sub.8 = -2.3442                                                              d.sub.8 = 0.0116                                                               r.sub.9 = 2.4393                                                               d.sub.9 = 0.7777 n.sub.5 = 1.69680                                                                          ν.sub. 5 = 55.52                               r.sub.10 = -4.4832                                                             d.sub.10 = 0.4755                                                              r.sub.11 = -1.1857                                                             d.sub.11 = 0.3582                                                                               n.sub.6 = 1.72825                                                                          ν.sub.6 = 28.46                                r.sub.12 = -1.8661                                                             d.sub.12 = 0.9316                                                              r.sub.13 = ∞                                                             d.sub.13 = 0.3582                                                                               n.sub.7 = 1.51633                                                                          ν.sub.7 = 64.15                                r.sub.14 = ∞                                                             ______________________________________                                         |h.sub.1 /f.sub.1 | = 0.8187, 1.15|h.sub.4          /f.sub.4 | = 0.1215                                                   f.sub.2 = 2.171, f.sub.1 = -1.288, f.sub.23 = 1.482                            f.sub.a /f.sub.b = 13.805/2.171 = 6.359, R.sub.2 = 3.4686                      R.sub.2 ' = -2.7135, R.sub.3 = -1.9941                                         ______________________________________                                    

where, reference symbols r₁, r₂, . . . respectively represent radii of curvature of respective lens surfaces, reference symbols d₁, d₂, . . . respectively represent thicknesses of respective lenses and airspaces between respective lenses, reference symbols n₁, n₂, . . . respectively represent refractive indices of respective lenses, and reference symbols ν₁, ν₂, . . . respectively represent Abbe's numbers of respective lenses.
 14. An objective for an endoscope according to claim 5 having the following numerical data:

    ______________________________________                                         f =140  1, F.sub.No = 3.109, 2ω = 138.27°                         IH = 1.1424                                                                    ______________________________________                                         r.sub.1 = 5.7266                                                               d.sub.1 = 0.3579 n.sub.1 = 1.88300                                                                          ν.sub.1 = 40.78                                r.sub.2 = 0.8615                                                               d.sub.2 = 1.6801                                                               r.sub.3 = 1.7123                                                               d.sub.3 = 0.8102 n.sub.2 = 1.71300                                                                          ν.sub.2 = 53.84                                r.sub.4 = -3.5156                                                              d.sub.4 = 0.0039                                                               r.sub.5 = ∞ (aperture stop)                                              d.sub.5 = 0.0659                                                               r.sub.6 = 2.4711                                                               d.sub.6 = 0.6563 n.sub.3 = 1.51633                                                                          ν.sub.3 = 64.15                                r.sub.7 = -0.7133                                                              d.sub.7 = 0.2863 n.sub.4 = 1.80518                                                                          ν.sub.4 = 25.43                                r.sub.8 = -1.2246                                                              d.sub.8 = 0.0636                                                               r.sub.9 = ∞                                                              d.sub.9 = 0.1034 n.sub.5 = 1.53172                                                                          ν .sub.5 = 48.90                               r.sub.10 = ∞                                                             d.sub.10 = 0.1720                                                              r.sub.11 = -0.9620                                                             d.sub.11 = 0.2147                                                                               n.sub.6 = 1.72825                                                                          ν.sub.6 = 28.46                                r.sub.12 = -2.5078                                                             d.sub.12 = 0.0517                                                              r.sub.13 = 7.1019                                                              d.sub.13 = 0.5011                                                                               n.sub.7 = 1.51633                                                                          ν.sub.7 = 64.15                                r.sub.14 = -19.3899                                                            d.sub.14 = 0.7158                                                              r.sub.15 = ∞                                                             d.sub.15 = 0.3579                                                                               n.sub.8 = 1.51633                                                                          ν.sub.8 = 64.15                                r.sub.16 = ∞                                                             ______________________________________                                         |h.sub.1 /f.sub.1 | = 0.8129, 1.15|h.sub.4          /f.sub.4 | = 0.2031                                                   f.sub.2 = 1.726, f.sub.1 = -1.189 f.sub.23 = 1.262                             f.sub.a /f.sub.b = 10.132/1.726 = 5.870, R.sub.2 = 1.712                       R.sub.2 ' = -3.5156, R.sub.3 =  2.471                                          ______________________________________                                    

where, reference symbols r₁, r₂, . . . respectively represent radii of curvature of respective lens surfaces, reference symbols d₁, d₂, . . . respectively represent thicknesses of respective lenses and airspaces between respective lenses, reference symbols n₁, n₂, . . . respectively represent refractive indices of respective lenses, and reference symbols ν₁, ν₂, . . . respectively represent Abbe's number of respective lenses.
 15. An objective for an endoscope according to claim 5 having the following numerical data:

    ______________________________________                                         f = 1, F.sub.No = 3.085, 2ω = 139.536°                            IH = 1.2073                                                                    ______________________________________                                         r.sub.1 = 3.1833                                                               d.sub.1 = 0.3782 n.sub.1 = 1.88300                                                                          ν.sub.1 = 40.78                                r.sub.2 = 0.8334                                                               d.sub.2 = 1.7146                                                               r.sub.3 = 2.4300                                                               d.sub.3 = 0.7182 n.sub.2 = 1.71300                                                                          ν.sub.2 = 53.84                                r.sub.4 = -2.2325                                                              d.sub.4 = 0.0250                                                               r.sub.5 = ∞ (aperture stop)                                              d.sub.5 = 0.0546                                                               r.sub.6 = 7.1362                                                               d.sub.6 = 0.5463 n.sub.3 = 1.51633                                                                          ν.sub.3 = 64.15                                r.sub.7 = -0.7591                                                              d.sub.7 = 0.2185 n.sub.4 = 1.80518                                                                          ν.sub.4 = 25.43                                r.sub.8 = -1.2930                                                              d.sub.8 = 0.0672                                                               r.sub.9 = ∞                                                              d.sub.9 = 0.1092 n.sub.5 =  1.53172                                                                         ν.sub.5 = 48.90                                r.sub.10 = ∞                                                             d.sub.10 = 0.3020                                                              r.sub.11 = -0.8880                                                             d.sub.11 = 0.2731                                                                               n.sub.6 = 1.72825                                                                          ν.sub.6 = 28.46                                r.sub.12 = -1.1927                                                             d.sub.12 = 0.0546                                                              r.sub.13 = 10.5247                                                             d.sub.13 = 0.5295                                                                               n.sub.7 = 1.51633                                                                          ν.sub.7 = 64.15                                r.sub.14 = 117.0536                                                            d.sub.14 = 0.7564                                                              r.sub.15 = ∞                                                             d.sub.15 = 0.3782                                                                               n.sub.8 = 1.51633                                                                          ν.sub.8 = 64.15                                r.sub.16 = ∞                                                             ______________________________________                                         |h.sub.1 /h.sub.4 | = 0.8008, 1.15|h.sub.4          /f.sub.4 | = 0.0561                                                   f.sub.2 = 1.744, f.sub.1 = -1.383, f.sub.23 = 1.335                            f.sub.a /f.sub.b = 22.360/1.744 = 12.821, R.sub.2 = 2.430                      R.sub.2 ' = -2.2325, R.sub.3 = 7.136                                           ______________________________________                                    

where, reference symbols r₁, r₂, . . . respectively represent radii of curvature of respective lens surfaces, reference symbols d₁, d₂, . . . respectively represent thicknesses of respective lenses and airspaces between respective lenses, reference symbols n₁, n₂, . . . respectively represent refractive indices of respective lenses, and reference symbols ν₁, ν₂, . . . respectively represent Abbe's numbers of respective lenses.
 16. An objective for an endoscope according to claim 5 having the following numerical data:

    ______________________________________                                         f = 1, F.sub.No = 3.044, 2ω = 140.082°                            IH = 1.0969                                                                    ______________________________________                                         r.sub.1 = 5.4983                                                               d.sub.1 = 0.3436 n.sub.1 = 1.88300                                                                          ν.sub.1 = 40.78                                r.sub.2 = 0.8851                                                               d.sub.2 = 1.3387                                                               r.sub.3 = 3.1007                                                               d.sub.3 = 0.4124 n.sub.2 = 1.72342                                                                          ν.sub.2 = 37.95                                r.sub.4 = -6.9867                                                              d.sub.4 = 0.2456                                                               r.sub.5 = 6.4144                                                               d.sub.5 = 0.2062 n.sub.3 = 1.6980                                                                           ν.sub.3 = 55.52                                r.sub.6 = 2.4882                                                               d.sub.6 = 0.2368                                                               r.sub.7 = ∞ (aperture stop)                                              d.sub.7 = 0.0860                                                               r.sub.8 = 3.4511                                                               d.sub.8 = 0.8753 n.sub.4 = 1.65830                                                                          ν.sub.4 = 57.33                                r.sub.9 = -2.8298                                                              d.sub.9 = 0.0932                                                               r.sub.10 = 2.2130                                                              d.sub.10 = 0.7745                                                                               n.sub.5 = 1.6980                                                                           ν.sub.5 = 55.52                                r.sub.11 = -6.8452                                                             d.sub.11 = 0.4152                                                              r.sub.12 = -1.5863                                                             d.sub.12 = 0.3436                                                                               n.sub.6 = 1.72825                                                                          ν.sub.6 = 28.46                                r.sub.13 = -5.3578                                                             d.sub.13 = 0.8408                                                              r.sub.14 = ∞                                                             d.sub.14 = 0.3436                                                                               n.sub.7 = 1.51633                                                                          ν.sub.7 = 64.15                                r.sub.15 =                                                                     ______________________________________                                         |h.sub.1 /f.sub.1 | = 0.8288, 1.15|h.sub.4          /f.sub.4 | = 0.2126                                                   f.sub.2 = 5.060, f.sub.1 = -1.238, f.sub.23 = 1.513                            f.sub.a /f.sub.b = 3.020/2.487 = 1.214. R.sub.2 = 3.1007                       R.sub.2 ' = 2.4882, R.sub.3 = 3.4511                                           ______________________________________                                    

where, reference symbols r₁, r₂, . . . respectively represent radii of curvature of respective lens surfaces, reference symbols d₁, d₂, . . . respectively represent thicknesses of respective lenses and airspaces between respective lenses, reference symbols n₁, n₂, . . . respectively represent refractive indices of respective lenses, and reference symbols ν₁, ν₂, . . . respectively represent Abbe's numbers of respective lenses.
 17. An objective for an endoscope according to claim 5 having the following numerical data:

    ______________________________________                                         f = 1, F.sub.No = 3.027, 2ω= 132.72                                      IH = 1.1757                                                                    ______________________________________                                         r.sub.1 = 5.1635                                                               d.sub.1 = 0.3690 n.sub.1 = 1.88300                                                                          ν.sub.1 = 40.78                                r.sub.2 = 0.9388                                                               d.sub.2 = 0.6126                                                               r.sub.3 = 3.8306                                                               d.sub.3 = 0.2583 n.sub.2 = 1.77250                                                                          ν.sub.2 = 49.66                                r.sub.4 = 2.2149                                                               d.sub.4 = 0.9078                                                               r.sub.5 = 2.8179                                                               d.sub.5 = 0.5166 n.sub.3 = 1.72825                                                                          ν.sub.3 = 28.46                                r.sub.6 = -2.8179                                                              d.sub.6 = 0.0590                                                               r.sub.7 = ∞ (aperture stop)                                              d.sub.7 = 0.3247                                                               r.sub.8 = 4.9768                                                               d.sub.8 = 0.8119 n.sub.4 = 1.58913                                                                          ν.sub.4 = 60.97                                r.sub.9 = -0.8827                                                              d.sub.9 = 0.2952 n.sub.5 = 1.80518                                                                          ν.sub.5 = 25.43                                r.sub.10 = -2.0002                                                             d.sub.10 = 0.0738                                                              r.sub.11 = ∞                                                             d.sub.11 = 0.3690                                                                               n.sub.6 = 1.53172                                                                          ν.sub.6 = 48.90                                r.sub.12 = ∞                                                             d.sub.12 = 0.0738                                                              r.sub.13 = 3.0482                                                              d.sub.13 = 0.6274                                                                               n.sub.7 = 1.65160                                                                          ν.sub.7 = 58.52                                r.sub.14 = -5.5591                                                             d.sub.14 = 0.3026                                                              r.sub.15 = -1.5381                                                             d.sub.15 = 0.2214                                                                               n.sub.8 = 1.84666                                                                          ν.sub.8 = 23.78                                r.sub.16 = -11.0629                                                            d.sub.16 = 0.3247                                                              r.sub.17 = ∞                                                             d.sub.17 = 0.7381                                                                               n.sub.9 = 1.54869                                                                          ν.sub.9 = 45.55                                r.sub.18 = ∞                                                             ______________________________________                                         |h.sub.1 /f.sub.1 | = 0.7425, 1.15|h.sub.4          /f.sub.4 | = 0.3957                                                   f.sub.2 = 2.012, f.sub.1 = -1.031, f.sub.23  = 1.588                           f.sub.a /f.sub.b = 3.650/2.012 = 1.814, R.sub.2 = 2.8179                       R.sub.2 ' = -2.8179, R.sub.3 = 4.9768                                          ______________________________________                                    

where, reference symbols r₁, r₂, . . . respectively represent radii of curvature of respective lens surfaces, reference symbols d₁, d₂, . . . respectively represent thicknesses of respective lenses and airspaces between respective lenses, reference symbols n₁, n₂, . . . respectively represent refractive indices of respective lenses, and reference symbols ν₁, ν₂, . . . respectively represent Abbe's numbers of respective lenses.
 18. An objective for an endoscope according to claim 5 having the following numerical data:

    ______________________________________                                         f = 1, F.sub.No = 3.012 2ω = 140.0°                               IH = 1.197                                                                     ______________________________________                                         r.sub.1 = 5.9912                                                               d.sub.1 = 0.3750 n.sub.1 = 1.88300                                                                          ν.sub.1 = 40.78                                r.sub.2 = 0.9537                                                               d.sub.2 = 0.5250                                                               r.sub.3 = 3.7795                                                               d.sub.3 = 0.2250 n.sub.2 = 1.88300                                                                          ν.sub.2 = 40.78                                r.sub.4 = 2.2136                                                               d.sub.4 = 1.1585                                                               r.sub.5 = 2.5094                                                               d.sub.5 = 0.4591 n.sub.3 = 1.72825                                                                          ν.sub.3 = 28.46                                r.sub.6 = -3.7450                                                              d.sub.6 = 0.1125                                                               r.sub.7 = ∞ (aperture stop)                                              d.sub.7 = 0.3134                                                               r.sub.8 = 4.7584                                                               d.sub.8 = 0.7459 n.sub.4 = 1.58913                                                                          ν.sub.4 = 60.97                                r.sub.9 = -0.8785                                                              d.sub.9 = 0.3000 n.sub.5 = 1.80518                                                                          ν.sub.5 = 25.43                                r.sub.10 = -2.0123                                                             d.sub.10 = 0.4069                                                              r.sub.11 = 5.0897                                                              d.sub.11 = 0.5250                                                                               n.sub.6 = 1.65830                                                                          ν.sub.6 = 57.33                                r.sub.12 = -4.6412                                                             d.sub.12 = 0.3298                                                              r.sub.13 = -1.4135                                                             d.sub.13 = 0.2250                                                                               n.sub.7 = 1.80518                                                                          ν.sub.7 = 25.43                                r.sub.14 = -3.4758                                                             d.sub.14 = 0.0088                                                              r.sub.15 = ∞                                                             d.sub.15 = 0.0750                                                                               n.sub.8 = 1.51633                                                                          ν.sub.8 = 64.15                                r.sub.16 = ∞                                                             d.sub.16 = 0.7500                                                              r.sub.17 = ∞                                                             d.sub.17 = 0.3750                                                                               n.sub.9 = 1.51633                                                                          ν.sub.9 = 64.15                                r.sub.18 = ∞                                                             ______________________________________                                         |h.sub.1 /f.sub.1 | = 0.8141, 1.15|h.sub.4          /f.sub.4 | = 0.2636                                                   f.sub.2 = 2.129, f.sub.1  = -1.002, f.sub.23 = 1.636                           f.sub.a /f.sub.b = 3.768/2.129 = 1.770, R.sub.2 = 2.5094                       R.sub.2 ' = -3.7450, R.sub.3 = 4.7584                                          ______________________________________                                    

where, reference symbols r₁, r₂, . . . respectively represent radii of curvature of respective lens surfaces, reference symbols d₁, d₂, . . . respectively represent thicknesses of respective lenses and airspaces between respective lenses, reference symbols n₁, n₂, . . . respectively represent refractive indices of respective lenses, and reference symbols ν₁, ν₂, . . . respectively represent Abbe's numbers of respective lenses.
 19. An objective for an endoscope according to claim 1 wherein at least one aspherical surface is provided in at least one of a front subsystem located in front of said aperture stop and a rear subsystem located in rear of said aperture stop.
 20. An objective for an endoscope according to claim 19 wherein each of said aspherical surfaces has a shape expressed by the formula shown below when the optical axis is designated as the x axis and a straight line, which is perpendicular to the optical axis and which passes the intersecting point between said aspherical surface and optical axis, is designated as the y axis: ##EQU7## where, reference symbol C represents the inverse number of the radius of curvature of the spherical surface which is in contact with said aspherical surface at a position near the optical axis, reference sumbol P represents a parameter representing the shape of said aspherical surface, and reference symbols B, E, F, G, . . . respectively represent the coefficients of aspherical surface of the second order, fourth order, sixth order, eighth order and so on,and wherein said objective for an endoscope has the following numerical data:

    ______________________________________                                         f = 1, F.sub.No = 3.001, 2ω = 120.832°                            IH = 1.2267                                                                    ______________________________________                                         r.sub.1 = 5.9125 (aspherical surface)                                          d.sub.1 = 0.3843   n.sub.1 = 1.88300                                                                         ν.sub.1 = 40.78                               r.sub.2 = 0.8298                                                               d.sub.2 = 0.9897                                                               r.sub.3 = ∞                                                              d.sub.3 = 0.3843   n.sub.2 = 1.53172                                                                         ν.sub.2 = 48.90                               r.sub.4 = ∞                                                              d.sub.4 = 0.1845                                                               r.sub.5 = 2.9048                                                               d.sub.5 = 0.5380   n.sub.3 = 1.72825                                                                         ν.sub.3 = 28.46                               r.sub.6 = -2.9283                                                              d.sub.6 = 0.1313                                                               r.sub.7 = ∞ (aperture stop)                                              d.sub.7 = 0.2910                                                               r.sub.8 = 5.4055                                                               d.sub.8 = 0.7010   n.sub.4 = 1.58913                                                                         ν.sub.4 = 60.97                               r.sub.9 = -0.9380                                                              d.sub.9 = 0.3075   n.sub.5 = 1.80518                                                                         ν.sub.5 = 25.43                               r.sub.10 = -1.8953                                                             d.sub.10 = 0.2034                                                              r.sub.11 = 2.6198                                                              d.sub.11 = 0.5380  n.sub.6 = 1.65830                                                                         ν.sub.6 = 57.33                               r.sub.12 = -11.3821                                                            d.sub.12 = 0.3328                                                              r.sub.13 = -1.2309 (aspherical surface)                                        d.sub.13 = 0.2690  n.sub.7 = 1.80518                                                                         ν.sub.7 = 25.43                               r.sub.14 = -3.6160                                                             d.sub.14 = 0.3714                                                              r.sub.15 = ∞                                                             d.sub.15 = 0.7686  n.sub.8 = 1.54869                                                                         ν.sub.8 = 45.55                               r.sub.16 = ∞                                                             ______________________________________                                         |h.sub.1 /f.sub.1 | = 0.8266, 1.15|h.sub.4          /f.sub.4 | = 0.3411                                                   f.sub.2 = 2.083, f.sub.1 = -1.133, f.sub.23 = 1.452                            f.sub.a /f.sub.b = 3.285/2.083 = 1.577, R.sub.2 = 2.9048                       R.sub.2 ' =  -2.9283, R.sub.3 = 5.4055                                         coefficients of aspherical surfaces                                            (1st lens surface)                                                                            P = 1, E = 0.22631 × 10.sup.-1                            (13th lens surface)                                                                           P = 1,                                                          ______________________________________                                    

where, reference symbols r₁, r₂, . . . respectively represent radii of curvature of respective lens surfaces, reference symbols d₁, d₂, . . . respectively represent thicknesses of respective lenses and airspaces between respective lenses, reference symbols n₁, n₂, . . . respectively represent refractive indices of respective lenses, and reference symbols ν₁, ν₂, . . . respectively represent Abbe's numbers of respective lenses, of the coefficients of aspherical surface, those which are not shown in the numerical data are zero.
 21. An objective for an endoscope according to claim 19 wherein each of said aspherical surfaces has a shape expressed by the formula shown below when the optical axis is designated as the x axis and a straight line, which is perpendicular to the optical axis and which passes the intersecting point between said aspherical surface and optical axis, is designated as the y axis: ##EQU8## where, reference symbol C represents the inverse number of the radius of curvature of the spherical surface which is in contact with said aspherical surface at a position near the optical axis, reference symbol P represents a parameter representing the shape of said aspherical surface, and reference symbols B, E, F, G, . . . respectively represent the coefficients of aspherical surface of the second order, fourth order, sixth order, eighth order and so on,and wherein said objective for an endoscope has the following numerical data:

    ______________________________________                                         f = 1, F.sub.No = 3.004, 2ω = 120.07°                             IH = 2.4366                                                                    ______________________________________                                         r.sub.1 = 6.3333 (aspherical surface)                                          d.sub.1 = 0.3818   n.sub.1 = 1.88300                                                                         ν.sub.1 = 40.78                               r.sub.2 = 0.8893 (aspherical surface)                                          d.sub.2 = 1.8084                                                               r.sub.3 = 1.8590                                                               d.sub.3 = 0.9825   n.sub.2 = 1.71300                                                                         ν.sub.2 = 53.84                               r.sub.4 = -3.8279                                                              d.sub.4 = 0.0042                                                               r.sub.5 = ∞ (aperture stop)                                              d.sub.5 = 0.0767                                                               r.sub.6 = 2.7250                                                               d.sub.6 = 0.7392   n.sub.3 = 1.51633                                                                         ν.sub.3 = 64.15                               r.sub.7 = -0.7605                                                              d.sub.7 = 0.3054   n.sub.4 = 1.80518                                                                         ν.sub.4 = 25.43                               r.sub.8 = -1.3061                                                              d.sub.8 = 0.3156                                                               r.sub.9 = -1.0055                                                              d.sub.9 = 0.2290   n.sub.5 = 1.72825                                                                         ν.sub.5 = 28.46                               r.sub.10 = -2.2630                                                             d.sub.10 = 0.0552                                                              r.sub.11 = 7.1359                                                              d.sub.11 = 0.5346  n.sub.6 = 1.51633                                                                         ν.sub.6 = 64.15                               r.sub.12 = -8.5566 (aspherical surface)                                        d.sub.12 = 0.7636                                                              r.sub.13 = ∞                                                             d.sub.13 = 0.3818  n.sub.7 = 1.51633                                                                         ν.sub.7 = 64.15                               r.sub.14 = ∞                                                             ______________________________________                                         |h.sub.1 /f.sub.1 | = 0.9051, 1.15|h.sub.4          /f.sub.4 | = 0.1536                                                   f.sub.2 = 1.891, f.sub.1 = -1.212, f.sub.23 = 1.404                            f.sub.a /f.sub.b = 7.6241/1.891 = 4.032, R.sub.2 = 1.8590                      R.sub.2 ' = -3.8279, R.sub.3 = 2.7250                                          coefficients of aspherical surfaces                                            (1st lens surface)                                                                            P = 0, E = 0.15726 × 10.sup.-1                            (2nd lens surface)                                                                            P= 1,                                                           (12th lens surface)                                                                           P= 1                                                            ______________________________________                                    

where, reference symbols r₁, r₂, . . . respectively represent radii of curvature of respective lens surfaces, reference symbols d₁, d₂, . . . respectively represent thicknesses of respective lenses and airspaces between respective lenses, reference symbols n₁, n₂, . . . respectively represent refractive indices of respective lenses, and reference symbols ν₁, ν₂, . . . respectively represent Abbe's numbers of respective lenses, of the coefficients of aspherical surface, those which are not shown in the numerical data are zero.
 22. An objective for an endoscope according to claim 19 fulfilling the conditions (15) and (17) shown below:

    A.sub.F ·A.sub.R <0                               (15)

    0.01<|A.sub.F /A.sub.R |<20              (17)

where, ##EQU9## where reference symbol AF_(i) represents the value obtained when the coefficient of astigmatism A to be caused by the deviation of the aspherical surface, which is formed on ith surface out of respective lens surfaces in said front subsystem, from the spherical surface is divided by F number, and reference symbol A_(Fj) represents the value obtained when the coefficient of astigmatism A to be caused by the deviation of the aspherical surface, which is formed on jth surface out of respective lens surfaces in said rear subsystem, from the spherical surface is divided by F number.
 23. An objective for an endoscope according to claim 22 wherein each of said aspherical surfaces has a shape expressed by the formula shown below when the optical axis is designated as the x axis and a straight line, which is perpendicular to the optical axis and which passes the intersecting point between said aspherical surface and optical axis, is designated as the y axis: ##EQU10## where, reference symbol C represents the inverse number of the radius of curvature of the spherical surface which is in contact with said aspherical surface at a position near the optical axis, reference symbol P represents a parameter representing the shape of said aspherical surface, and reference symbols B, E, F, G, . . . respectively represent the coefficients of aspherical surface of the second order, fourth order, sixth order, eighth order and so on,and wherein said objective for an endoscope has the following numerical data:

    ______________________________________                                         f = 1, F.sub.No = 2.998,  2ω = 120.796°                           IH = 1.2469                                                                    ______________________________________                                         r.sub.1 = 5.9663 (aspherical surface)                                          d.sub.1 = 0.3906                                                                              n.sub.1 = 1.88300                                                                           ν.sub.1 = 40.78                                 r.sub.2 = 0.8272                                                               d.sub.2 = 1.0070                                                               r.sub.3 = ∞                                                              d.sub.3 = 0.3906                                                                              n.sub.2 = 1.53172                                                                           ν.sub.2 = 48.90                                 r.sub.4 = ∞                                                              d.sub.4 = 0.1875                                                               r.sub.5 = 3.0194                                                               d.sub.5 = 0.5469                                                                              n.sub.3 = 1.72825                                                                           ν.sub.3 = 28.46                                 r.sub.6 = -2.9267                                                              d.sub.6 = 0.1334                                                               r.sub.7 = ∞ (aperture stop)                                              d.sub.7 = 0.2955                                                               r.sub.8 = 5.6257                                                               d.sub.8 = 0.7125                                                                              n.sub.4 = 1.58913                                                                           ν.sub.4 = 60.97                                 r.sub.9 = -0.9698                                                              d.sub.9 = 0.3125                                                                              n.sub.5 = 1.80518                                                                           ν.sub.5 = 25.43                                 r.sub.10 = -1.9298                                                             d.sub.10 = 0.2068                                                              r.sub.11 = 2.5655                                                              d.sub.11 = 0.5469                                                                             n.sub.6 = 1.65830                                                                           ν.sub.6 = 57.33                                 r.sub.12 = -12.9642                                                            d.sub.12 = 0.3383                                                              r.sub.13 = -1.2924 (aspherical surface)                                        d.sub.13 = 0.2734                                                                             n.sub.7 = 1.80518                                                                           ν.sub.7 = 25.43                                 r.sub.14 = -4.2008                                                             d.sub.14 = 0.3775                                                              r.sub.15 = ∞                                                             d.sub.15 = 0.7813                                                                             n.sub.8 = 1.54869                                                                           ν.sub.8 = 45.55                                 r.sub.16 = ∞                                                             ______________________________________                                         |h.sub.1 /f.sub.1 | = 0.8444, 1.15|h.sub.4          /f.sub.4 | = 0.3481                                                   f.sub.2 = 2.123, f.sub.1 = -1.128, f.sub.23 = 1.469                            f.sub.a /f.sub.b = 3.358/2.123 = 1.582, R.sub.2 =  3.0194                      R.sub.2 ' = -2.9267, R.sub.3 = 5.6257                                          coefficients of aspherical surfaces                                            (1st lens surface)                                                                            P = 1, E = 0.24015 × 10.sup.-1                            (13th lens surface)                                                                           P = 1, E = -0.12297 × 10.sup.-1                            ##STR5##                                                                      ______________________________________                                    

where, reference symbols r₁, r₂, . . . respectively represent radii of curvature of respective lens surfaces, reference symbols d₁, d₂, . . . respectively represent thicknesses of respective lenses and airspaces between respective lenses, reference symbols n₁, n₂, . . . respectively represent refractive indices of respective lenses, and reference symbols ν₁, ν₂, . . . respectively represent Abbe's numbers of respective lenses, of the coefficients of aspherical surface, those which are not shown in the numerical data are zero.
 24. An objective for an endoscope according to claim 23 wherein each of said aspherical surfaces has a shape expressed by the formula shown below when the optical axis is designated as the x axis and a straight line, which is perpendicular to the optical axis and which passes the intersecting point between said aspherical surface and optical axis, is designated as the y axis: ##EQU11## where, reference symbol C represents the inverse number of the radius of curvature of the spherical surface which is in contact with said aspherical surface at a position near the optical axis, reference symbol P represents a parameter representing the shape of said aspherical surface, and reference symbols B, E, F, G, . . . respectively represent the coefficients of aspherical surface of the second order, fourth order, sixth order, eighth order and so on,and wherein said objective for an endoscope has the following numerical data:

    ______________________________________                                         f = 1, F.sub.No = 3.030, 2ω = 99.99°                              IH = 1.1466                                                                    ______________________________________                                         r.sub.1 = 6.0105                                                               d.sub.1 = 0.3592                                                                              n.sub.1 = 1.88300                                                                           ν.sub.1 = 40.78                                 r.sub.2 = 0.8194 (aspherical surface)                                          d.sub.2 = 0.7184                                                               r.sub.3 = 9.2577                                                               d.sub.3 = 0.3592                                                                              n.sub.2 = 1.53172                                                                           ν.sub.2 = 48.90                                 r.sub.4 = -30.2947                                                             d.sub.4 = 0.3879                                                               r.sub.5 = 2.6624                                                               d.sub.5 = 0.5029                                                                              n.sub.3 = 1.72825                                                                           ν.sub.3 = 28.46                                 r.sub.6 = -3.7679                                                              d.sub.6 = 0.1252                                                               r.sub.7 = ∞ (aperture stop)                                              d.sub.7 = 0.2740                                                               r.sub.8 = 4.8937                                                               d.sub.8 = 0.6552                                                                              n.sub.4 = 1.58913                                                                           ν.sub.4 = 60.97                                 r.sub.9 =  -0.8923                                                             d.sub.9 = 0.2874                                                                              n.sub.5 = 1.80518                                                                           ν.sub.5 = 25.43                                 r.sub.10 = -1.5847                                                             d.sub.10 = 0.1901                                                              r.sub.11 = 2.5445                                                              d.sub.11 = 0.5029                                                                             n.sub.6 = 1.65830                                                                           ν.sub.6 = 57.33                                 r.sub.12 = -34.1731                                                            d.sub.12 = 0.3000                                                              r.sub.13 = -1.3263                                                             d.sub.13 = 0.2514                                                                             n.sub.7 = 1.80518                                                                           ν.sub.7 = 25.43                                 r.sub.14 = -7.5450 (aspherical surface)                                        d.sub.14 = 0.3471                                                              r.sub.15 = ∞                                                             d.sub.15 = 0.7184                                                                             n.sub.8 = 1.54869                                                                           ν.sub.8 = 45.55                                 r.sub.16 = ∞                                                             ______________________________________                                         |h.sub.1 /f.sub.1 | = 0.4335, 1.15|h.sub.4          /f.sub.4 | = 0.3286                                                   f.sub.2 = 1.989, f.sub.1 = -1.110, f.sub.23 = 1.406                            f.sub.a /f.sub.b =  13.378/2.215 = 6.048,  R.sub.2 = 9.2577                    R.sub.2 ' = -3.7679, R.sub.3 = 4.894                                           coefficients of aspherical surfaces                                            (2nd lens surface)                                                                            P = 0, E = 0.51666 × 10.sup.-1                                           F = 0.13710                                                     (14th lens surface)                                                                           P = 0, E = 0.17323                                               ##STR6##                                                                      ______________________________________                                    

where, reference symbols r₁, r₂, . . . respectively represent radii of curvature of respective lens surfaces, reference symbols d₁, d₂, . . . respectively represent thicknesses of respective lenses and airspaces between respective lenses, reference symbols n₁, n₂, . . . respectively represent refractive indices of respective lenses, and reference symbols ν₁, ν₂, . . . respectively represent Abbe's numbers of respective lenses, of the coefficients of aspherical surface, those which are not shown in the numerical data are zero.
 25. An objective for an endoscope according to claim 23, wherein each of said aspherical surfaces has a shape expressed by the formula shown below when the optical axis is designated as the x axis and a straight line, which is perpendicular to the optical axis and which passes the intersecting point between said aspherical surface and optical axis, is designated as the y axis: ##EQU12## where, reference symbol C represents the inverse number of the radius of curvature of the spherical surface which is in contact with said aspherical surface at a position near the optical axis, reference symbol P represents a parameter representing the shape of said aspherical surface, and reference symbols B, E, F, G, . . . respectively represent the coefficients of aspherical surface of the second order, fourth order, sixth order, eighth order and so on,and wherein said objective for an endoscope has the following numerical data:

    ______________________________________                                         f = 1, F.sub.No = 3.008, 2ω = 129.582°                            IH = 1.2449                                                                    ______________________________________                                         r.sub.1 = 7.0922 (aspherical surface)                                          d.sub.1 = 0.3901                                                                              n.sub.1 = 1.88300                                                                           ν.sub.1 = 40.78                                 r.sub.2 = 0.9320 (aspherical surface)                                          d.sub.2 = 1.8376                                                               r.sub.3 = 1.9116                                                               d.sub.3 = 0.9886                                                                              n.sub.2 = 1.71300                                                                           ν.sub.2 = 53.84                                 r.sub.4 = -3.8101                                                              d.sub.4 = 0.0043                                                               r.sub.5 = ∞ (aperture stop)                                              d.sub.5 = 0.0800                                                               r.sub.6 = 2.9288                                                               d.sub.6 = 0.7605                                                                              n.sub.3 = 1.51633                                                                           ν.sub.3 = 64.15                                 r.sub.7 = -0.7899                                                              d.sub.7 = 0.3121                                                                              n.sub.4 = 1.80518                                                                           ν.sub.4 = 25.43                                 r.sub.8 = -1.3346                                                              d.sub.8 = 0.3051                                                               r.sub.9 = -1.0142                                                              d.sub.9 = 0.2340                                                                              n.sub.5 = 1.72825                                                                           ν.sub.5 = 28.46                                 r.sub.10 = -2.2485                                                             d.sub.10 = 0.0564                                                              r.sub.11 = 6.3079                                                              d.sub.11 = 0.5462                                                                             n.sub.6 = 1.51633                                                                           ν.sub.6 = 64.15                                 r.sub.12 = -6.2050 (aspherical surface)                                        d.sub.12 = 0.7803                                                              r.sub.13 = ∞                                                             d.sub.13 = 0.3901                                                                             n.sub.7 = 1.51633                                                                           ν.sub.7 = 64.15                                 r.sub.14 = ∞                                                             ______________________________________                                         |h.sub.1 /f.sub.1 | = 0.8950, 1.15|h.sub.4          /f.sub.4 | = 0.1226                                                   f.sub.2 = 1.924, f.sub.1 = -1.252, f.sub.23 = 1.435                            f.sub.a /f.sub.b = 6.150/1.924 = 3.196, R.sub.2 = 1.9116                       R.sub.2 ' = -3.8101, R.sub.3 = 2.9288                                          coefficients of aspherical surfaces                                            (1st lens surface)                                                                            P =  0, E = 0.12860 × 10.sup.-1                           (2nd lens surface)                                                                            P = 1,                                                          (12th lens surface)                                                                           P = 1, E = 0.29866 × 10.sup.-1                             ##STR7##                                                                      ______________________________________                                    

where, reference symbols r₁, r₂, . . . respectively represent radii of curvature of respective lens surfaces, reference symbols d₁, d₂, . . . respectively represent thicknesses of respective lenses and airspaces between respective lenses, reference symbols n₁, n₂, . . . respectively represent refractive indices of respective lenses, and reference symbols ν₁, ν₂, . . . respectively represent Abbe's numbers of respective lenses, of the coefficients of aspherical surface, those which are not shown in the numerical data are zero.
 26. An objective for an endoscope according to claim 23 wherein each of said aspherical surfaces has a shape expressed by the formula shown below when the optical axis is designated as the x axis and a straight line, which is perpendicular to the optical axis and which passes the intersecting point between said aspherical surface and optical axis, is designated as the y axis: ##EQU13## where, reference symbol C represents the inverse number of the radius of curvature of the spherical surface which is in contact with said aspherical surface at a position near the optical axis, reference symbol P represents a parameter representing the shape of said aspherical surface, and reference symbols B, E, F, G, . . . respectively represent the coefficients of aspherical surface of the second order, fourth order, sixth order, eighth order and so on,and wherein said objective for an endoscope has the following numerical data:

    ______________________________________                                         f = 1, F.sub.No = 2.996, 2ω = 110.0°                              IH = 1.2040                                                                    ______________________________________                                         r.sub.1 = 3.9397 (aspherical surface)                                          d.sub.1 = 0.3772                                                                              n.sub.1 = 1.88300                                                                           ν.sub.1 = 40.78                                 r.sub.2 = 0.7949                                                               d.sub.2 = 0.6186                                                               r.sub.3 = 6.9234                                                               d.sub.3 = 0.2640                                                                              n.sub.2 = 1.77250                                                                           ν.sub.2 = 49.66                                 r.sub.4 = 4.1093                                                               d.sub.4 = 0.9559                                                               r.sub.5 = 2.7606                                                               d.sub.5 = 0.5281                                                                              n.sub.3 = 1.72825                                                                           ν.sub.3 = 28.46                                 r.sub.6 = -2.2016                                                              d.sub.6 = 0.0754                                                               r.sub.7 = ∞ (aperture stop)                                              d.sub.7 = 0.3167                                                               r.sub.8 = 17.2715                                                              d.sub.8 = 0.8298                                                                              n.sub.4 = 1.58913                                                                           ν.sub.4 = 60.97                                 r.sub.9 = -0.8495                                                              d.sub.9 = 0.3018                                                                              n.sub. 5 = 1.80518                                                                          ν.sub.5 = 25.43                                 r.sub.10 = -2.4692                                                             d.sub.10 = 0.0754                                                              r.sub.11 = ∞                                                             d.sub.11 = 0.3772                                                                             n.sub.6 = 1.53172                                                                           ν.sub.6 = 48.90                                 r.sub.12 = ∞                                                             d.sub.12 = 0.0754                                                              r.sub.13 = 2.1704                                                              d.sub.13 = 0.6412                                                                             n.sub.7 = 1.65160                                                                           ν.sub.7 = 58.52                                 r.sub.14 = -23.8501                                                            d.sub.14 = 0.3103                                                              r.sub.15 = -1.5651                                                             d.sub.15 = 0.2263                                                                             n.sub.8 = 1.84666                                                                           ν.sub.8 = 23.78                                 r.sub.16 = -5.0483 (aspherical surface)                                        d.sub.16 = 0.3163                                                              r.sub.17 = ∞                                                             d.sub.17 = 0.7544                                                                             n.sub.9 = 1.54869                                                                           ν.sub.9 = 45.55                                 r.sub.18 = ∞                                                             ______________________________________                                         |h.sub.1 /f.sub.1 | = 0.7355, 1.15|h.sub.4          /f.sub.4 |  = 0.3202                                                  f.sub.2 = 1.761, f.sub.1 = -1.033, f.sub.23 = 1.642                            f.sub.a /f.sub.b = 8.594/1.761 = 4.880, R.sub.2 = 2.7606                       R.sub.2 ' = -2.2016, R.sub.3 = 17.2715                                         coefficients of aspherical surfaces                                            (1st lens surface)                                                                            P = 1, E = 0.25038 × 10.sup.-1                                           F = 0.45776 × 10.sup.-2                                   (16th lens surface)                                                                           P = 1, E = 0.23705 × 10.sup.-1                             ##STR8##                                                                      ______________________________________                                    

where, reference symbols r₁, r₂, . . . respectively represent radii of curvature of respective lens surfaces, reference symbols d₁, d₂, . . . respectively represent thicknesses of respective lenses and airspaces between respective lenses, reference symbols n₁, n₂, . . . respectively represent refractive indices of respective lenses, and reference symbols ν₁, ν₂, . . . respectively represent Abbe's numbers of respective lenses, of the coefficients of aspherical surface, those which are not shown in the numerical data are zero.
 27. An objective for an endoscope according to claim 19 fulfilling the condition (22) shown below:

    0≦Q.sub.h <4                                        (22)

where, the value of Q_(h) is obtained by the formula Q_(h) =|Q_(S) /Q_(M) | wherein the value of Q_(S) is obtained by the formula Q_(S) =Q_(F) +Q_(R) wherein reference symbol Q_(F) represents the sum of Q_(i) in said front subsystem, and reference symbol Q_(R) represents the sum of Q_(i) in said rear subsystem, the value of Q_(i) being calculated by the formula

    Q.sub.i =(N.sub.i -N.sub.i+1){Eh.sub.i.sup.2 +Fh.sub.i.sup.4 +Gh.sub.i.sup.6 +. . . }

wherein reference symbol N_(i) represents the refractive index of the medium existing on the object side of ith surface, and reference symbol N_(i+1) represents the refractive index of the medium existing on the image side of ith surface, reference symbol Q_(M) representing either Q_(F) or Q_(R) which has the larger absolute value out of them.
 28. An objective for an endoscope according to claim 27 wherein each of said aspherical surfaces has a shape expressed by the formula shown below when the optical axis is designated as the x axis and a straight line, which is perpendicular to the optical axis and which passes the intersecting point between said aspherical surface and optical axis, is designated as the y axis: ##EQU14## where, reference symbol C represents the inverse number of the radius of curvature of the spherical surface which is in contact with said aspherical surface at a position near the optical axis, reference symbol P represents a parameter representing the shape of said aspherical surface, and reference symbols B, E, F, G, . . . respectively represent the coefficients of aspherical surface of the second order, fourth order, sixth order, eighth order and so on,and wherein said objective for an endoscope has the following numerical data:

    ______________________________________                                         f = 1,  F.sub.No = 3.035, 2ω= 140.02°                             IH = 1.6295                                                                    ______________________________________                                         r.sub.1 = 5.8908                                                               d.sub.1 = 0.5105   n.sub.1 = 1.88300                                                                         ν.sub.1 = 40.78                               r.sub.2 = 1.5830 (aspherical surface)                                          d.sub.2 = 2.1049                                                               r.sub.3 = 7.1003                                                               d.sub.3 = 0.7497   n.sub.2 = 1.72342                                                                         ν.sub.2 = 37.95                               r.sub.4 = -6.1767                                                              d.sub.4 = 0.0056                                                               r.sub.5 = ∞ (aperture stop)                                              d.sub.5 = 0.1188                                                               r.sub.6 = 12.6805                                                              d.sub.6 = 0.9930   n.sub.3 = 1.65830                                                                         ν.sub.3 = 57.33                               r.sub.7 = -1.2573                                                              d.sub.7 = 0.4084   n.sub.4 = 1.80518                                                                         ν.sub.4 = 25.43                               r.sub.8 = -2.0394                                                              d.sub.8 = 0.2964                                                               r.sub.9 = -1.4831                                                              d.sub.9 = 0.3063   n.sub.5 =  1.84666                                                                        ν.sub.5 = 23.78                               r.sub.10 = -1.6611                                                             d.sub.10 = 0.1532                                                              r.sub.11 = 8.1827                                                              d.sub.11 = 0.7147  n.sub.6 = 1.51633                                                                         ν.sub.6 = 64.15                               r.sub.12 = -1.8839 (aspherical surface)                                        d.sub.12 = 1.0291                                                              r.sub.13 = ∞                                                             d.sub.13 = 0.5105  n.sub.7 = 1.51633                                                                         ν.sub.7 = 64.15                               r.sub.14 = ∞                                                             ______________________________________                                         |h.sub.1 /f.sub.1 |= 0.6747, 1.15|h.sub.4           /f.sub.4 |= 0.3865                                                    f.sub.2 = 4.677, f.sub.1 = -2.596, f.sub.23 = 2.168                            f.sub.a /f.sub.b = 4.677/3.039 = 1.539, R.sub.2 = 7.01003                      R.sub.2 '= -6.1767, R.sub.3 = 12.6805                                          coefficients of aspherical surfaces                                            (2nd lens surface)                                                                            P = 1, E = 0.59267 × 10.sup.-1                                           F = -0.29531 × 10.sup.-1                                  (12th lens surface)                                                                           P = 1, E = 0.10652                                              Qh = 1.1459                                                                    ______________________________________                                    

where, reference symbols r₁, r₂, . . . respectively represent radii of curvature of respective lens surfaces, reference symbols d₁, d₂, . . . respectively represent thicknesses of respective lenses and airspaces between respective lenses, reference symbols n₁, n₂, . . . respectively represent refractive indices of respective lenses, and reference symbols ν₁, ν₂, . . . respectively represent Abbe's numbers of respective lenses, of the coefficients of aspherical surface, those which are not shown in the numerical data are zero.
 29. An objective for an endoscope according to claim 27 wherein each of said aspherical surfaces has a shape expressed by the formula shown below when the optical axis is designated as the x axis and a straight line, which is perpendicular to the optical axis and which passes the intersecting point between said aspherical surface and optical axis, is designated as the y axis: ##EQU15## where, reference symbol C represents the inverse number of the radius of curvature of the spherical surface which is in contact with said aspherical surface at a position near the optical axis, reference symbol P represents a parameter representing the shape of said aspherical surface, and reference symbols B, E, F, G, . . . respectively represent the coefficients of aspherical surface of the second order, fourth order, sixth order, eighth order and so on,and wherein said objective for an endoscope has the following numerical data:

    ______________________________________                                         f = 1, F.sub.No = 3.032, 1ω= 140.0°                               IH = 1.4229                                                                    ______________________________________                                         r.sub.1 = 5.6068                                                               d.sub.1 = 0.4458   n.sub.1 = 1.88300                                                                         ν.sub.1 = 40.78                               r.sub.2 = 1.2801 (aspherical surface)                                          d.sub.2 = 2.0273                                                               r.sub.3 = 3.6331                                                               d.sub.3 = 0.7592   n.sub.2 = 1.72342                                                                         ν.sub.2 = 37.95                               r.sub.4 = -5.0124                                                              d.sub.4 = 0.0049                                                               r.sub.5 = ∞ (aperture stop)                                              d.sub.5 = 0.1026                                                               r.sub.6 = 7.4259                                                               d.sub.6 = 0.8539   n.sub.3 = 1.65830                                                                         ν.sub.3 = 57.33                               r.sub.7 = -1.1844                                                              d.sub.7 = 0.3566   n.sub.4 = 1.80518                                                                         ν.sub.4 = 25.43                               r.sub.8 = -1.7581                                                              d.sub.8 = 0.3181                                                               r.sub.9 = -1.2303                                                              d.sub.9 = 0.2675   n.sub.5 =  1.84666                                                                        ν.sub.5 = 23.78                               r.sub.10 = -1.6302                                                             d.sub.10 = 0.1337                                                              r.sub.11 = 50.6667                                                             d.sub.11 = 0.6241  n.sub.6 = 1.51633                                                                         ν.sub.6 = 64.15                               r.sub.12 = -2.1201 (aspherical surface)                                        d.sub.12 = 0.8985                                                              r.sub.13 = ∞                                                             d.sub.13 = 0.4458  n.sub.7 = 1.51633                                                                         ν.sub.7 = 64.15                               r.sub.14 = ∞                                                             ______________________________________                                         |h.sub.1 /f.sub.1 | = 0.7323, 1.15|h.sub.4          /f.sub.4 | = 0.1542                                                   f.sub.2 = 3.023, f.sub.1 = -1.974, f.sub.23 = 1.662                            f.sub.a /f.sub.b = 3.957/2.439 = 1.622, R.sub.2 = 3.6331                       R.sub.2 ' = -5.0124, R.sub.3 = 7.4259                                          coefficients of aspherical surfaces                                            (2nd lens surface)                                                                            P = 1, E = 0.61335 × 10.sup.-1                                           F = -0.39851 × 10.sup.-1                                  (12th lens surface)                                                                           P = 1, E = 0.10463                                              Q.sub.h = 1.3035                                                               ______________________________________                                    

where, reference symbols r₁, r₂, . . . respectively represent radii of curvature of respective lens surfaces, reference symbols d₁, d₂, . . . respectively represent thicknesses of respective lenses and airspaces between respective lenses, reference symbols n₁, n₂, . . . respectively represent refractive indices of respective lenses, and reference symbols ν₁, ν₂, . . . respectively represent Abbe's numbers of respective lenses, of the coefficients of aspherical surface, those which are not shown in the numerical data are zero.
 30. An objective for an endoscope according to claim 27 wherein each of said aspherical surfaces has a shape expressed by the formula shown below when the optical axis is designated as the x axis and a straight line, which is perpendicular to the optical axis and which passes the intersecting point between said aspherical surface and optical axis, is designated as the y axis: ##EQU16## where, reference symbol C represents the inverse number of the radius of curvature of the spherical surface which is in contact with said aspherical surface at a position near the optical axis, reference symbol P represents a parameter representing the shape of said aspherical surface, and reference symbols B, E, F, G, . . . respectively represent the coefficients of aspherical surface of the second order, fourth order, sixth order, eighth order and so on,and wherein said objective for an endoscope has the following numerical data:

    ______________________________________                                         f = 1, F.sub.No = 3.033, 2ω= 140.01°                              IH = 1.4387                                                                    ______________________________________                                         r.sub.1 = 4.1525                                                               d.sub.1 = 0.4507   n.sub.1 = 1.88300                                                                         ν.sub.1 = 40.78                               r.sub.2 = 1.2907 (aspherical surface)                                          d.sub.2 = 1.9824                                                               r.sub.3 = 6.0185                                                               d.sub.3 = 0.6489   n.sub.2 = 1.72342                                                                         ν.sub.2 = 37.95                               r.sub.4 = -5.3701                                                              d.sub.4 = 0.0050                                                               r.sub.5 = ∞ (aperture stop)                                              d.sub.5 = 0.0988                                                               r.sub.6 = 9.8733                                                               d.sub.6 = 0.7706   n.sub.3 = 1.65830                                                                         ν.sub.3 = 57.33                               r.sub.7 = 2.1176                                                               d.sub.7 = 0.3606   n.sub.4 = 1.80518                                                                         ν.sub.4 = 25.43                               r.sub.8 = -1.7128                                                              d.sub.8 = 0.3216                                                               r.sub.9 = -1.6356                                                              d.sub.9 = 0.2704   n.sub.5 = 1.84666                                                                         ν.sub.5 =  23.78                              r.sub.10 = -1.6634 (aspherical surface)                                        d.sub.10 = 0.1352                                                              r.sub.11 = -3.0982                                                             d.sub.11 = 0.6310  n.sub.6 = 1.51633                                                                         ν.sub.6 = 64.15                               r.sub.12 = -1.5977 (aspherical surface)                                        d.sub.12 = 0.9086                                                              r.sub.13 = ∞                                                             d.sub.13 = 0.4507  n.sub.7 = 1.51633                                                                         ν.sub.7 = 64.15                               r.sub.14 = ∞                                                             ______________________________________                                         |h.sub.1 /f.sub.1 | = 0.6803, 1.15|h.sub.4          /f.sub.4 | = 0.1969                                                   f.sub.2 = 4.019, f.sub.1 = -2.290, f.sub.23 = 1.664                            f.sub.a /f.sub.b = 33.391/2.198 = 15.192, R.sub.2 = 6.0185                     R.sub.2 ' = -5.3701, R.sub.3 = 9.8733                                          coefficients of aspherical surfaces                                            (2nd lens surface)                                                                            P = 1, E = 0.64518 × 10.sup.-1                                           F = -0.38100 × 10.sup.-1                                  (10th lens surface)                                                                           P = 1, E = 0.10921                                              (12th lens surface)                                                                           P = 1, E = 0.82721 × 10.sup.-2                            Qh = 1.3030                                                                    ______________________________________                                    

where, reference symbols r₁, r₂, . . . respectively represent radii of curvature of respective lens surfaces, reference symbols d₁, d₂, . . . respectively represent thicknesses of respective lenses and airspaces between respective lenses, reference symbols n₁, n₂, . . . respectively represent refractive indices of respective lenses, and reference symbols ν₁, ν₂, . . . respectively represent Abbe's numbers of respective lenses, of the coefficients of aspherical surface, those which are not shown in the numerical data are zero. 